Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

abdominal aorta – portion of the aorta inferior to the aortic hiatus and superior to the common iliac arteries.

abdominopelvic cavity – division of the anterior (ventral) cavity that houses the abdominal and pelvic viscera.

abducens nerve – sixth cranial nerve; responsible for contraction of one of the extraocular muscles.

abduction – movement in the coronal plane that moves a limb laterally away from the body; spreading of the fingers.

ABO blood group – blood-type classification based on the presence or absence of A and B carbohydrates on the erythrocyte membrane surface.

absolute refractory period – time during an action period when another action potential cannot be generated because the voltage-gated Na+ channel is inactivated.

absorption – passage of digested products from the intestinal lumen through mucosal cells and into the bloodstream or lacteals.

accessory digestive organ – includes teeth, tongue, salivary glands, gallbladder, liver, and pancreas.

accessory duct – (also, duct of Santorini) duct that runs from the pancreas into the duodenum.

acclimatisation – process of adjustment that the respiratory system makes due to chronic exposure to high altitudes.

acetabular labrum – lip of fibrocartilage that surrounds outer margin of the acetabulum on the hip bone.

acetabulum – large, cup-shaped cavity located on the lateral side of the hip bone; formed by the junction of the ilium, pubis, and ischium portions of the hip bone.

acetylcholine (ACh) – neurotransmitter that binds at a motor end-plate to trigger depolarisation.

acinus – cluster of glandular epithelial cells in the pancreas that secretes pancreatic secretion in the pancreas.

acne – skin condition due to infected sebaceous glands.

acromegaly – disorder in adults caused when abnormally high levels of GH trigger growth of bones in the face, hands, and feet.

acromial end of the clavicle – lateral end of the clavicle that articulates with the acromion of the scapula.

acromial process – acromion of the scapula.

acromioclavicular joint – articulation between the acromion of the scapula and the acromial end of the clavicle.

acromion – flattened bony process that extends laterally from the scapular spine to form the bony tip of the shoulder.

acrosome – cap-like vesicle located at the anterior-most region of a sperm that is rich with lysosomal enzymes capable of digesting the protective layers surrounding the oocyte.

acrosomal reaction – release of digestive enzymes by sperm that enables them to burrow through the corona radiata and penetrate the zona pellucida of an oocyte prior to fertilisation.

actin – protein that makes up most of the thin myofilaments in a sarcomere muscle fibre.

action potential – change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibres.

activation gate – part of the voltage-gated Na+ channel that opens when the membrane voltage reaches threshold.

active immunity – immunity developed from an individual’s own immune system.

active transport – form of transport across the cell membrane that requires input of cellular energy.

acute inflammation – inflammation occurring for a limited time period; rapidly developing.

acute mountain sickness (AMS) – condition that occurs a result of acute exposure to high altitude due to a low partial pressure of oxygen.

adaptive immune response – relatively slow but very specific and effective immune response controlled by lymphocytes.

adductor tubercle – small, bony bump located on the superior aspect of the medial epicondyle of the femur.

adenylyl cyclase – membrane-bound enzyme that converts ATP to cyclic AMP, creating cAMP, as a result of G-protein activation.

α-dextrin – breakdown product of starch.

α-dextrinase – brush border enzyme that acts on α-dextrins.

adipocytes – lipid storage cells.

adipose tissue – specialised areolar tissue rich in stored fat.

adrenal artery – branch of the abdominal aorta; supplies blood to the adrenal (suprarenal) glands.

adrenal cortex – outer region of the adrenal glands consisting of multiple layers of epithelial cells and capillary networks that produces mineralocorticoids and glucocorticoids.

adrenal glands – endocrine glands located at the top of each kidney that are important for the regulation of the stress response, blood pressure and blood volume, water homeostasis, and electrolyte levels.

adrenal medulla – inner layer of the adrenal glands that plays an important role in the stress response by producing adrenaline and noradrenaline.

adrenal vein – drains the adrenal or suprarenal glands that are immediately superior to the kidneys; the right adrenal vein enters the inferior vena cava directly and the left adrenal vein enters the left renal vein.

adrenaline – primary and most potent catecholamine hormone secreted by the adrenal medulla in response to short-term stress.

adrenocorticotropic hormone (ACTH) – anterior pituitary hormone that stimulates the adrenal cortex to secrete corticosteroid hormones (also called corticotropin).

aerobic respiration – production of ATP in the presence of oxygen.

afferent lymphatic vessels – lead into a lymph node.

afterload – force the ventricles must develop to effectively pump blood against the resistance in the vessels.

agglutination – clustering of cells into masses linked by antibodies.

agranular leukocytes – leukocytes with few visible granules in their cytoplasm; specifically, monocytes, lymphocytes, and NK cells.

ala – (plural = alae) small, flaring structure of a nostril that forms the lateral side of the nares.

alar cartilage – cartilage that supports the apex of the nose and helps shape the nares; it is connected to the septal cartilage and connective tissue of the alae.

alarm reaction – the short-term stress, or the fight-or-flight response, of stage one of the general adaptation syndrome mediated by the hormones adrenaline and noradrenaline.

alar plate – developmental region of the spinal cord that gives rise to the posterior horn of the grey matter.

albinism – genetic disorder that affects the skin, in which there is no melanin production.

albumin – most abundant plasma protein, accounting for most of the osmotic pressure of plasma.

aldosterone – hormone produced and secreted by the adrenal cortex that stimulates sodium and fluid retention and increases blood volume and blood pressure.

alkaloid – substance, usually from a plant source, that is chemically basic with respect to pH and will stimulate bitter receptors.

allantois – finger-like outpocketing of yolk sac forms the primitive excretory duct of the embryo; precursor to the urinary bladder.

alpha cell – pancreatic islet cell type that produces the hormone glucagon.

alpha-helix structure (α-helix) – type of secondary protein structure formed by folding the polypeptide into a helix shape with hydrogen bonds stabilising the structure.

alveolar dead space – air space within alveoli that are unable to participate in gas exchange.

alveolar duct – small tube that leads from the terminal bronchiole to the respiratory bronchiole and is the point of attachment for alveoli.

alveolar macrophage – immune system cell of the alveolus that removes debris and pathogens.

alveolar pore – opening that allows airflow between neighbouring alveoli.

alveolar process of the mandible – upper border of mandibular body that contains the lower teeth.

alveolar process of the maxilla – curved, inferior margin of the maxilla that supports and anchors the upper teeth.

alveolar sac – cluster of alveoli.

alveoli – (of the breast) milk-secreting cells in the mammary gland.

alveolus – small, grape-like sac that performs gas exchange in the lungs.

amacrine cell – type of cell in the retina that connects to the bipolar cells near the outer synaptic layer and provides the basis for early image processing within the retina.

amino acid – a protein’s monomer; has a central carbon or alpha carbon to which an amino group, a carboxyl group, a hydrogen, and an R group or side chain is attached; the R group is different for all 20 common amino acids.

amnion – transparent membranous sac that encloses the developing foetus and fills with amniotic fluid.

amniotic cavity – cavity that opens between the inner cell mass and the trophoblast; develops into amnion.

aminopeptidase – brush border enzyme that acts on proteins.

amphiarthrosis – slightly mobile joint.

amphipathic – descr.ibes a molecule that exhibits a difference in polarity between its two ends, resulting in a difference in water solubility.

ampulla – in the ear, the structure at the base of a semicircular canal that contains the hair cells and cupula for transduction of rotational movement of the head.

ampulla – (of the uterine tube) middle portion of the uterine tube in which fertilisation often occurs

amygdala – nucleus deep in the temporal lobe of the cerebrum that is related to memory and emotional behaviour.

anaemia – deficiency of red blood cells or haemoglobin.

anagen – active phase of the hair growth cycle.

anal canal – final segment of the large intestine.

anal column – long fold of mucosa in the anal canal.

anal sinus – recess between anal columns.

anaphase – third stage of mitosis (and meiosis), during which sister chromatids separate into two new nuclear regions of a dividing cell.

anaphylactic shock – type of shock that follows a severe allergic reaction and results from massive vasodilation.

anastomosis – (plural = anastomoses) area where vessels unite to allow blood to circulate even if there may be partial blockage in another branch.

anatomical dead space – air space present in the airway that never reaches the alveoli and therefore never participates in gas exchange.

anatomical neck – line on the humerus located around the outside margin of the humeral head.

anatomical position – standard reference position used for describing locations and directions on the human body.

anatomical sphincter – smooth or skeletal muscle surrounding the lumen of a vessel or hollow organ that can restrict flow when contracted

anatomy – science that studies the form and composition of the body’s structures.

anchoring junction – mechanically attaches adjacent cells to each other or to the basement membrane.

angioblasts – stem cells that give rise to blood vessels.

angiogenesis – development of new blood vessels from existing vessels.

angiotensin-converting enzyme – the enzyme that c.

angle of the mandible – rounded corner located at outside margin of the body and ramus junction.

angle of the rib – portion of rib with greatest curvature; together, the rib angles form the most posterior extent of the thoracic cage.

angiotensin-converting enzyme (ACE) – enzyme produced by the lungs that catalyses the reaction of inactive angiotensin I into active angiotensin II.

angiotensin I – protein produced by the enzymatic action of renin on angiotensinogen; inactive precursor of angiotensin II.

angiotensin II – protein produced by the enzymatic action of ACE on inactive angiotensin I; actively causes vasoconstriction and stimulates aldosterone release by the adrenal cortex.

angiotensinogen – inactive protein in the circulation produced by the liver; precursor of angiotensin I; must be modified by the enzymes renin and ACE to be activated.

ankle joint – joint that separates the leg and foot portions of the lower limb; formed by the articulations between the talus bone of the foot inferiorly, and the distal end of the tibia, medial malleolus of the tibia, and lateral malleolus of the fibula superiorly.

annular ligament – intrinsic ligament of the elbow articular capsule that surrounds and supports the head of the radius at the proximal radioulnar joint.

anosmia – loss of the sense of smell; usually the result of physical disruption of the first cranial nerve.

aqueous humour – watery fluid that fills the anterior chamber containing the cornea, iris, ciliary body, and lens of the eye.

anterior – describes the front or direction toward the front of the body; also referred to as ventral.

anterior arch – anterior portion of the ring-like C1 (atlas) vertebra.

anterior border of the tibia – narrow, anterior margin of the tibia that extends inferiorly from the tibial tuberosity.

anterior cardiac veins – vessels that parallel the small cardiac arteries and drain the anterior surface of the right ventricle; bypass the coronary sinus and drain directly into the right atrium.

anterior cavity – larger body cavity located anterior to the posterior (dorsal) body cavity; includes the serous membrane-lined pleural cavities for the lungs, pericardial cavity for the heart, and peritoneal cavity for the abdominal and pelvic organs; also referred to as ventral cavity.

anterior cerebral artery – arises from the internal carotid artery; supplies the frontal lobe of the cerebrum.

anterior column – white matter between the anterior horns of the spinal cord composed of many different groups of axons of both ascending and descending tracts.

anterior communicating artery – anastomosis of the right and left internal carotid arteries; supplies blood to the brain.

anterior corticospinal tract – division of the corticospinal pathway that travels through the ventral (anterior) column of the spinal cord and controls axial musculature through the medial motor neurons in the ventral (anterior) horn.

anterior cranial fossa – shallowest and most anterior cranial fossa of the cranial base that extends from the frontal bone to the lesser wing of the sphenoid bone.

anterior cruciate ligament – intracapsular ligament of the knee; extends from anterior, superior surface of the tibia to the inner aspect of the lateral condyle of the femur; resists hyperextension of knee.

anterior horn – grey matter of the spinal cord containing multipolar motor neurons, sometimes referred to as the ventral horn.

anterior inferior iliac spine – small, bony projection located on the anterior margin of the ilium, below the anterior superior iliac spine.

anterior interventricular artery – (also, left anterior descending artery or LAD) major branch of the left coronary artery that follows the anterior interventricular sulcus.

anterior interventricular sulcus – sulcus located between the left and right ventricles on the anterior surface of the heart.

anterior longitudinal ligament – ligament that runs the length of the vertebral column, uniting the anterior aspects of the vertebral bodies.

anterior median fissure – deep midline feature of the anterior spinal cord, marking the separation between the right and left sides of the cord.

anterior sacroiliac ligament – strong ligament between the sacrum and the ilium portions of the hip bone that supports the anterior side of the sacroiliac joint.

anterior spinal artery – blood vessel from the merged branches of the vertebral arteries that runs along the anterior surface of the spinal cord.

anterior superior iliac spine – rounded, anterior end of the iliac crest.

anterior talofibular ligament – intrinsic ligament located on the lateral side of the ankle joint, between talus bone and lateral malleolus of fibula; supports talus at the talocrural joint and resists excess inversion of the foot.

anterior tibial artery – branches from the popliteal artery; supplies blood to the anterior tibial region; becomes the dorsalis pedis artery.

anterior tibial vein – forms from the dorsal venous arch; drains the area near the tibialis anterior muscle and leads to the popliteal vein.

anterior (ventral) sacral foramen – one of the series of paired openings located on the anterior (ventral) side of the sacrum.

antibodies – (also, immunoglobulins or gamma globulins) antigen-specific proteins produced by specialised B lymphocytes that protect the body by binding to foreign objects such as bacteria and viruses.

anticoagulant – substance such as heparin that opposes coagulation.

anticodon – consecutive sequence of three nucleotides on a tRNA molecule that is complementary to a specific codon on an mRNA molecule.

antidiuretic hormone (ADH) – hypothalamic hormone that is stored by the posterior pituitary and that signals the kidneys to reabsorb water.

antigen – molecule recognised by the receptors of B and T lymphocytes.

antigenic determinant – (also, epitope) one of the chemical groups recognised by a single type of lymphocyte antigen receptor.

antigen presentation – binding of processed antigen to the protein-binding cleft of a major histocompatibility complex molecule.

antigen processing – internalisation and digestion of antigen in an antigen-presenting cell.

antigen receptor – two-chain receptor by which lymphocytes recognise antigen.

angiogenesis – formation of blood capillary networks.

antithrombin – anticoagulant that inactivates factor X and opposes the conversion of prothrombin (factor II) into thrombin in the common pathway.

antrum – fluid-filled chamber that characterises a mature tertiary (antral) follicle.

anulus fibrosus – tough, fibrous outer portion of an intervertebral disc, which is strongly anchored to the bodies of the adjacent vertebrae.

anuria – absence of urine produced; production of 50 mL or less per day.

aorta – largest artery in the body, originating from the left ventricle and descending to the abdominal region where it bifurcates into the common iliac arteries at the level of the fourth lumbar vertebra; arteries originating from the aorta distribute blood to virtually all tissues of the body.

aortic arch – arc that connects the ascending aorta to the descending aorta; ends at the intervertebral disk between the fourth and fifth thoracic vertebrae.

aortic hiatus – opening in the diaphragm that allows passage of the thoracic aorta into the abdominal region where it becomes the abdominal aorta.

aortic sinuses – small pockets in the ascending aorta near the aortic valve that are the locations of the baroreceptors (stretch receptors) and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis.

aortic valve – (also, aortic semilunar valve) valve located at the base of the aorta.

apex – tip of the external nose.

apical – that part of a cell or tissue which, in general, faces an open space.

apical ectodermal ridge – enlarged ridge of ectoderm at the distal end of a limb bud that stimulates growth and elongation of the limb.

apneustic centre – network of neurons within the pons that stimulate the neurons in the dorsal respiratory group; controls the depth of inspiration.

apocrine secretion – release of a substance along with the apical portion of the cell.

aponeurosis – broad, tendon-like sheet of connective tissue that attaches a skeletal muscle to another skeletal muscle or to a bone.

apoptosis – programmed cell death.

apocrine sweat gland – type of sweat gland that is associated with hair follicles in the armpits and genital regions.

appendicular skeleton – all bones of the upper and lower limbs, plus the girdle bones that attach each limb to the axial skeleton.

appendix – (vermiform appendix) coiled tube attached to the cecum.

aquaporin – protein-forming water channels through the lipid bilayer of the cell; allows water to cross; activation in the collecting ducts is under the control of ADH.

arachnoid granulation – out-pocket of the arachnoid membrane into the dural sinuses that allows for reabsorption of CSF into the blood.

arachnoid mater – middle layer of the meninges named for the spider-web–like trabeculae that extend between it and the pia mater.

arachnoid trabeculae – filaments between the arachnoid and pia mater within the subarachnoid space.

arcuate line of the ilium – smooth ridge located at the inferior margin of the iliac fossa; forms the lateral portion of the pelvic brim.

areola – highly pigmented, circular area surrounding the raised nipple and containing areolar glands that secrete fluid important for lubrication during suckling.

areolar tissue – (also, loose connective tissue) a type of connective tissue proper that shows little specialisation with cells dispersed in the matrix.

arm – region of the upper limb located between the shoulder and elbow joints; contains the humerus bone.

arrector pili – smooth muscle that is activated in response to external stimuli that pull on hair follicles and make the hair “stand up”.

arterial circle – (also, circle of Willis) anastomosis located at the base of the brain that ensures continual blood supply; formed from branches of the internal carotid and vertebral arteries; supplies blood to the brain.

arteriole – (also, resistance vessel) very small artery that leads to a capillary.

arteriovenous anastomosis – short vessel connecting an arteriole directly to a venule and bypassing the capillary beds.

artery – blood vessel that conducts blood away from the heart; may be a conducting or distributing vessel.

articular capsule – connective tissue structure that encloses the joint cavity of a synovial joint.

articular cartilage – thin layer of cartilage covering an epiphysis; reduces friction and acts as a shock absorber.

articular disc – meniscus; a fibrocartilage structure found between the bones of some synovial joints; provides padding or smooths movements between the bones; strongly unites the bones together.

articular tubercle – smooth ridge located on the inferior skull, immediately anterior to the mandibular fossa.

articulation – where two bone surfaces meet.

artificial pacemaker – medical device that transmits electrical signals to the heart to ensure that it contracts and pumps blood to the body.

ascending aorta – initial portion of the aorta, rising from the left ventricle for a distance of approximately 5 cm.

ascending tract – central nervous system fibres carrying sensory information from the spinal cord or periphery to the brain.

ascending colon – first region of the colon.

ascending pathway – fibre structure that relays sensory information from the periphery through the spinal cord and brain stem to other structures of the brain.

association area – region of cortex connected to a primary sensory cortical area that further processes the information to generate more complex sensory perceptions.

astrocyte – star-shaped cell in the central nervous system that regulates ions and uptake and/or breakdown of some neurotransmitters and contributes to the formation of the blood-brain barrier.

atmospheric pressure – amount of force that is exerted by gases in the air surrounding any given surface.

atlantoaxial joint – series of three articulations between the atlas (C1) vertebra and the axis (C2) vertebra, consisting of the joints between the inferior articular processes of C1 and the superior articular processes of C2, and the articulation between the dens of C2 and the anterior arch of C1.

atlanto-occipital joint – articulation between the occipital condyles of the skull and the superior articular processes of the atlas (C1 vertebra).

atlas – first cervical (C1) vertebra.

ATPase – enzyme that hydrolyses ATP to ADP.

atrial natriuretic peptide (ANP) – peptide hormone produced by the walls of the atria in response to high blood pressure, blood volume, or blood sodium that reduces the reabsorption of sodium and water in the kidneys and promotes vasodilation.

atrial reflex – (also, called Bainbridge reflex) autonomic reflex that responds to stretch receptors in the atria that send impulses to the cardioaccelerator area to increase HR when venous flow into the atria increases.

atrioventricular bundle – (also, bundle of His) group of specialised myocardial conductile cells that transmit the impulse from the AV node through the interventricular septum; form the left and right atrioventricular bundle branches.

atrioventricular bundle branches – (also, left or right bundle branches) specialised myocardial conductile cells that arise from the bifurcation of the atrioventricular bundle and pass through the interventricular septum; lead to the Purkinje fibres and also to the right papillary muscle via the moderator band.

atrioventricular (AV) node – clump of myocardial cells located in the inferior portion of the right atrium within the atrioventricular septum; receives the impulse from the SA node, pauses, and then transmits it into specialised conducting cells within the interventricular septum.

atrioventricular septum – cardiac septum located between the atria and ventricles; atrioventricular valves are located here.

atrioventricular valves – one-way valves located between the atria and ventricles; the valve on the right is called the tricuspid valve, and the one on the left is the mitral or bicuspid valve.

atrium – (plural = atria) upper or receiving chamber of the heart that pumps blood into the lower chambers just prior to their contraction; the right atrium receives blood from the systemic circuit that flows into the right ventricle; the left atrium receives blood from the pulmonary circuit that flows into the left ventricle.

atrophy – loss of mass and function.

audition – sense of hearing.

auricle – extension of an atrium visible on the superior surface of the heart.

auricle – fleshy external structure of the ear.

auricular surface of the ilium – roughened area located on the posterior, medial side of the ilium of the hip bone; articulates with the auricular surface of the sacrum to form the sacroiliac joint.

autocrine – chemical signal that elicits a response in the same cell that secreted it.

autolysis – breakdown of cells by their own enzymatic action.

autonomic nervous system (ANS) – functional division of the nervous system that is responsible for homeostatic reflexes that coordinate control of cardiac and smooth muscle, as well as glandular tissue.

autonomic tone – contractile state during resting cardiac activity produced by mild sympathetic and parasympathetic stimulation.

autophagy – lysosomal breakdown of a cell’s own components.

autorhythmicity – ability of cardiac muscle to initiate its own electrical impulse that triggers the mechanical contraction that pumps blood at a fixed pace without nervous or endocrine control.

axial skeleton – central, vertical axis of the body, including the skull, vertebral column, and thoracic cage.

axillary artery – continuation of the subclavian artery as it penetrates the body wall and enters the axillary region; supplies blood to the region near the head of the humerus (humeral circumflex arteries); the majority of the vessel continues into the brachium and becomes the brachial artery.

axillary nerve – systemic nerve of the arm that arises from the brachial plexus.

axillary vein – major vein in the axillary region; drains the upper limb and becomes the subclavian vein.

axis – second cervical (C2) vertebra.

axon – single process of the neuron that carries an electrical signal (action potential) away from the cell body toward a target cell.

axon hillock – tapering of the neuron cell body that gives rise to the axon.

axon segment – single stretch of the axon insulated by myelin and bounded by nodes of Ranvier at either end (except for the first, which is after the initial segment, and the last, which is followed by the axon terminal).

axon terminal – end of the axon, where there are usually several branches extending toward the target cell.

axoplasm – cytoplasm of an axon, which is different in composition than the cytoplasm of the neuronal cell body.

azygos vein – originates in the lumbar region and passes through the diaphragm into the thoracic cavity on the right side of the vertebral column; drains blood from the intercostal veins, oesophageal veins, bronchial veins, and other veins draining the mediastinal region; leads to the superior vena cava.

B

Bachmann’s bundle – (also, interatrial band) group of specialised conducting cells that transmit the impulse directly from the SA node in the right atrium to the left atrium.

Bainbridge reflex – (also, called atrial reflex) autonomic reflex that responds to stretch receptors in the atria that send impulses to the cardioaccelerator area to increase HR when venous flow into the atria increases.

ball-and-socket joint – synovial joint formed between the spherical end of one bone (the ball) that fits into the depression of a second bone (the socket); found at the hip and shoulder joints; functionally classified as a multiaxial joint.

baroreceptor reflex – autonomic reflex in which the cardiac centres monitor signals from the baroreceptor stretch receptors and regulate heart function based on blood flow.

barrier defences – antipathogen defences deriving from a barrier that physically prevents pathogens from entering the body to establish an infection.

Bartholin’s glands – (also, greater vestibular glands) glands that produce a thick mucus that maintains moisture in the vulva area; also referred to as the greater vestibular glands.

basal cell – type of stem cell found in the stratum basale and in the hair matrix that continually undergoes cell division, producing the keratinocytes of the epidermis.

basal cell carcinoma – cancer that originates from basal cells in the epidermis of the skin.

basal forebrain – nuclei of the cerebrum related to modulation of sensory stimuli and attention through broad projections to the cerebral cortex, loss of which is related to Alzheimer’s disease.

basal lamina – thin extracellular layer that lies underneath epithelial cells and separates them from other tissues.

basal nuclei – nuclei of the cerebrum (with a few components in the upper brain stem and diencephalon) that are responsible for assessing cortical movement commands and comparing them with the general state of the individual through broad modulatory activity of dopamine neurons; largely related to motor functions, as evidenced through the symptoms of Parkinson’s and Huntington’s diseases.

basal plate – developmental region of the spinal cord that gives rise to the lateral and anterior horns of grey matter.

base of the metatarsal bone – expanded, proximal end of each metatarsal bone.

basement membrane – in epithelial tissue, a thin layer of fibrous material that anchors the epithelial tissue to the underlying connective tissue; made up of the basal lamina and reticular lamina.

basilar artery – formed from the fusion of the two vertebral arteries; sends branches to the cerebellum, brain stem, and the posterior cerebral arteries; the main blood supply to the brain stem.

basilar membrane – in the ear, the floor of the cochlear duct on which the organ of Corti sits.

basilic vein – superficial vein of the arm that arises from the palmar venous arches, intersects with the median cubital vein, parallels the ulnar vein, and continues into the upper arm; along with the brachial vein, it leads to the axillary vein.

basophils – granulocytes that stain with a basic (alkaline) stain and store histamine and heparin.

B cells – lymphocytes that act by differentiating into an antibody-secreting plasma cell.

bedsore – sore on the skin that develops when regions of the body start necrotising due to constant pressure and lack of blood supply; also called decubitis ulcers.

beta cell – pancreatic islet cell type that produces the hormone insulin.

beta-pleated sheet (β-pleated) – secondary structure in proteins in which hydrogen bonding forms “pleats” between atoms on the polypeptide chain’s backbone.

Betz cells – output cells of the primary motor cortex that cause musculature to move through synapses on cranial and spinal motor neurons.

biaxial joint – type of diarthrosis; a joint that allows for movements within two planes (two axes).

bicipital groove – intertubercular groove; narrow groove located between the greater and lesser tubercles of the humerus.

bicuspid valve – (also, mitral valve or left atrioventricular valve) valve located between the left atrium and ventricle; consists of two flaps of tissue.

bile – alkaline solution produced by the liver and important for the emulsification of lipids.

bile canaliculus – small duct between hepatocytes that collects bile.

bilirubin – yellowish bile pigment produced when iron is removed from haem and the remaining molecule is further broken down into waste products.

biliverdin – green bile pigment produced during the conversion of non-iron haem to bilirubin.

binocular depth cues – indications of the distance of visual stimuli on the basis of slight differences in the images projected onto either retina.

biogenic amine – class of neurotransmitters that are enzymatically derived from amino acids but no longer contain a carboxyl group.

biological macromolecule – large molecule necessary for life that is built from smaller organic molecules.

bipolar – shape of a neuron with two processes extending from the neuron cell body—the axon and one dendrite.

bipolar cell – cell type in the retina that connects the photoreceptors to the RGCs.

blastocoel – fluid-filled cavity of the blastocyst.

blastocyst – term for the conceptus at the developmental stage that consists of about 100 cells shaped into an inner cell mass that is fated to become the embryo and an outer trophoblast that is fated to become the associated foetal membranes and placenta.

blastomere – daughter cell of a cleavage.

blood – liquid connective tissue composed of cellular components—erythrocytes, leukocytes, and platelets—and a fluid extracellular matrix called plasma; component of the cardiovascular system.

blood-brain barrier (BBB) – physiological barrier between the circulatory system and the central nervous system that establishes a privileged blood supply, restricting the flow of substances into the CNS.

blood colloidal osmotic pressure (BCOP) – pressure exerted by colloids suspended in blood within a vessel; a primary determinant is the presence of plasma proteins.

blood hydrostatic pressure – force blood exerts against the walls of a blood vessel or heart chamber.

blood flow – movement of blood through a vessel, tissue, or organ that is usually expressed in terms of volume per unit of time.

blood islands – masses of developing blood vessels and formed elements from mesodermal cells scattered throughout the embryonic disc.

blood pressure – force exerted by the blood against the wall of a vessel or heart chamber; can be described with the more generic term hydrostatic pressure.

blood–testis barrier – tight junctions between Sertoli cells that prevent bloodborne pathogens from gaining access to later stages of spermatogenesis and prevent the potential for an autoimmune reaction to haploid sperm.

blood typing or grouping – blood test for identification of blood type using commercially prepared antibodies and small samples of blood.

B lymphocytes – (also, B cells) lymphocytes that defend the body against specific pathogens and thereby provide specific (or adaptive) immunity.

body – mid-portion of the stomach.

body of uterus – middle section of the uterus.

body of the rib – shaft portion of a rib..

Bohr effect – relationship between blood pH and oxygen dissociation from haemoglobin.

bolus – mass of chewed food.

bone – hard, dense connective tissue that forms the structural elements of the skeleton.

bone marrow – tissue found inside bones; the site of all blood cell differentiation and maturation of B lymphocytes.

bone marrow biopsy – diagnostic test of a sample of red bone marrow.

bone marrow transplant – treatment in which a donor’s healthy bone marrow with its stem cells replaces diseased or damaged bone marrow of a patient.

Bowman’s capsule – cup-shaped sack lined by a simple squamous epithelium (parietal surface) and specialised cells called podocytes (visceral surface) that participate in the filtration process; receives the filtrate which then passes on to the PCTs.

Boyle’s law – relationship between volume and pressure as described by the formula: P1V1 = P2V2.

brachial artery – continuation of the axillary artery in the brachium; supplies blood to much of the brachial region; gives off several smaller branches that provide blood to the posterior surface of the arm in the region of the elbow; bifurcates into the radial and ulnar arteries at the coronoid fossa.

brachial plexus – nerve plexus associated with the lower cervical spinal nerves and first thoracic spinal nerve.

brachial vein – deeper vein of the arm that forms from the radial and ulnar veins in the lower arm; leads to the axillary vein.

brachiocephalic artery – single vessel located on the right side of the body; the first vessel branching from the aortic arch; gives rise to the right subclavian artery and the right common carotid artery; supplies blood to the head, neck, upper limb, and wall of the thoracic region.

brachiocephalic vein – one of a pair of veins that form from a fusion of the external and internal jugular veins and the subclavian vein; subclavian, external and internal jugulars, vertebral, and internal thoracic veins lead to it; drains the upper thoracic region and flows into the superior vena cava.

brain – the large organ of the central nervous system composed of white and grey matter, contained within the cranium and continuous with the spinal cord.

brain case – portion of the skull that contains and protects the brain, consisting of the eight bones that form the cranial base and rounded upper skull.

brain stem – region of the adult brain that includes the midbrain, pons, and medulla oblongata and develops from the mesencephalon, metencephalon, and myelencephalon of the embryonic brain.

bridge – portion of the external nose that lies in the area of the nasal bones.

broad ligament – wide ligament that supports the uterus by attaching laterally to both sides of the uterus and pelvic wall.

Broca’s area – region of the frontal lobe associated with the motor commands necessary for speech production and located only in the cerebral hemisphere responsible for language production, which is the left side in approximately 95 percent of the population.

Brodmann’s areas – mapping of regions of the cerebral cortex based on microscopic anatomy that relates specific areas to functional differences, as described by Brodmann in the early 1900s.

bronchial artery – systemic branch from the aorta that provides oxygenated blood to the lungs in addition to the pulmonary circuit.

bronchial bud – structure in the developing embryo that forms when the laryngotracheal bud extends and branches to form two bulbous structures.

bronchial tree – collective name for the multiple branches of the bronchi and bronchioles of the respiratory system.

bronchial vein – drains the systemic circulation from the lungs and leads to the azygos vein.

bronchiole – branch of bronchi that are 1 mm or less in diameter and terminate at alveolar sacs.

bronchoconstriction – decrease in the size of the bronchiole due to contraction of the muscular wall.

bronchodilation – increase in the size of the bronchiole due to contraction of the muscular wall.

bronchus – tube connected to the trachea that branches into many subsidiaries and provides a passageway for air to enter and leave the lungs.

bronchus-associated lymphoid tissue (BALT) – lymphoid nodule associated with the respiratory tract.

brush border – fuzzy appearance of the small intestinal mucosa created by microvilli.

brush border – formed by microvilli on the surface of certain cuboidal cells; in the kidney it is found in the PCT; increases surface area for absorption in the kidney.

buffy coat – thin, pale layer of leukocytes and platelets that separates the erythrocytes from the plasma in a sample of centrifuged blood.

bulbourethral glands – (also, Cowper’s glands) glands that secrete a lubricating mucus that cleans and lubricates the urethra prior to and during ejaculation.

bulbus cordis – portion of the primitive heart tube that will eventually develop into the right ventricle.

bundle of His – (also, atrioventricular bundle) group of specialised myocardial conductile cells that transmit the impulse from the AV node through the interventricular septum; form the left and right atrioventricular bundle branches.

bursa – connective tissue sac containing lubricating fluid that prevents friction between adjacent structures, such as skin and bone, tendons and bone, or between muscles.

C

calcaneofibular ligament – intrinsic ligament located on the lateral side of the ankle joint, between the calcaneus bone and lateral malleolus of the fibula; supports the talus bone at the ankle joint and resists excess inversion of the foot.

calcaneus – heel bone; posterior, inferior tarsal bone that forms the heel of the foot.

calcitonin – peptide hormone produced and secreted by the parafollicular cells (C cells) of the thyroid gland that functions to decrease blood calcium levels.

calyces – cup-like structures receiving urine from the collecting ducts where it passes on to the renal pelvis and ureter.

callus – thickened area of skin that arises due to constant abrasion.

calmodulin – regulatory protein that facilitates contraction in smooth muscles.

calvaria – (also, skullcap) rounded top of the skull.

canaliculi – (singular = canaliculus) channels within the bone matrix that house one of an osteocyte’s many cytoplasmic extensions that it uses to communicate and receive nutrients.

capacitance – ability of a vein to distend and store blood.

capacitance vessels – veins.

capacitation – process that occurs in the female reproductive tract in which sperm are prepared for fertilisation; leads to increased motility and changes in their outer membrane that improve their ability to release enzymes capable of digesting an oocyte’s outer layers.

capillary – smallest of blood vessels where physical exchange occurs between the blood and tissue cells surrounded by interstitial fluid.

capillary bed – network of 10–100 capillaries connecting arterioles to venules.

capillary hydrostatic pressure (CHP) – force blood exerts against a capillary.

capitate – from the lateral side, the third of the four distal carpal bones; articulates with the scaphoid and lunate proximally, the trapezoid laterally, the hamate medially, and primarily with the third metacarpal distally.

capitulum – knob-like bony structure located anteriorly on the lateral, distal end of the humerus.

capsaicin – molecule that activates nociceptors by interacting with a temperature-sensitive ion channel and is the basis for “hot” sensations in spicy food.

carbaminohemoglobin – compound of carbon dioxide and haemoglobin, and one of the ways in which carbon dioxide is carried in the blood.

carbohydrate – biological macromolecule in which the ratio of carbon to hydrogen and to oxygen is 1:2:1; carbohydrates serve as energy sources and structural support in cells and form arthropods’ cellular exoskeleton.

carbonic anhydrase (CA) – enzyme that catalyses the reaction that causes carbon dioxide and water to form carbonic acid.

cardia – (also, cardiac region) part of the stomach surrounding the cardiac orifice (oesophageal hiatus).

cardiac cycle – period of time between the onset of atrial contraction (atrial systole) and ventricular relaxation (ventricular diastole).

cardiac muscle – heart muscle, under involuntary control, composed of striated cells that attach to form fibres, each cell contains a single nucleus, contracts autonomously.

cardiac notch – depression in the medial surface of the inferior lobe of the left lung where the apex of the heart is located.

cardiac output (CO) – volume of blood pumped by each ventricle during one minute; equals HR multiplied by SV.

cardiac plexus – paired complex network of nerve fibres near the base of the heart that receive sympathetic and parasympathetic stimulations to regulate HR.

cardiac reflexes – series of autonomic reflexes that enable the cardiovascular centres to regulate heart function based upon sensory information from a variety of visceral sensors.

cardiac reserve – difference between maximum and resting CO.

cardiac skeleton – (also, skeleton of the heart) reinforced connective tissue located within the atrioventricular septum; includes four rings that surround the openings between the atria and ventricles, and the openings to the pulmonary trunk and aorta; the point of attachment for the heart valves.

cardiogenic area – area near the head of the embryo where the heart begins to develop 18–19 days after fertilisation.

cardiogenic cords – two strands of tissue that form within the cardiogenic area.

cardiogenic shock – type of shock that results from the inability of the heart to maintain cardiac output.

cardiomyocyte – muscle cell of the heart.

carotid canal – zig-zag tunnel providing passage through the base of the skull for the internal carotid artery to the brain; begins anteromedial to the styloid process and terminates in the middle cranial cavity, near the posterior-lateral base of the sella turcica.

carotid sinuses – small pockets near the base of the internal carotid arteries that are the locations of the baroreceptors and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis.

carpal bone – one of the eight small bones that form the wrist and base of the hand; these are grouped as a proximal row consisting of (from lateral to medial) the scaphoid, lunate, triquetrum, and pisiform bones, and a distal row containing (from lateral to medial) the trapezium, trapezoid, capitate, and hamate bones.

carpal tunnel – passageway between the anterior forearm and hand formed by the carpal bones and flexor retinaculum.

carpometacarpal joint – articulation between one of the carpal bones in the distal row and a metacarpal bone of the hand.

cartilage – semi-rigid connective tissue found on the skeleton in areas where flexibility and smooth surfaces support movement.

cartilaginous joint – joint at which the bones are united by hyaline cartilage (synchondrosis) or fibrocartilage (symphysis).

catagen – transitional phase marking the end of the anagen phase of the hair growth cycle.

cauda equina – bundle of spinal nerve roots that descend from the lower spinal cord below the first lumbar vertebra and lie within the vertebral cavity; has the appearance of a horse’s tail.

caudal – describes a position below or lower than another part of the body proper; near or toward the tail (in humans, the coccyx, or lowest part of the spinal column); also referred to as inferior.

caudate – nucleus deep in the cerebrum that is part of the basal nuclei; along with the putamen, it is part of the striatum.

cavernous sinus – enlarged vein that receives blood from most of the other cerebral veins and the eye socket, and leads to the petrosal sinus.

cecum – pouch forming the beginning of the large intestine.

cell – smallest independently functioning unit of all organisms; in animals, a cell contains cytoplasm, composed of fluid and organelles.

cell cycle – life cycle of a single cell, from its birth until its division into two new daughter cells.

cell junction – point of cell-to-cell contact that connects one cell to another in a tissue.

cell membrane – membrane surrounding all animal cells, composed of a lipid bilayer interspersed with various molecules; also known as plasma membrane.

cellular components (formed elements) – cellular components of blood; that is, erythrocytes, leukocytes, and platelets.

cellulose – polysaccharide that comprises the plants’ cell wall; provides structural support to the cell.

cementum – bone-like tissue covering the root of a tooth.

central canal – longitudinal channel in the centre of each osteon; contains blood vessels, nerves, and lymphatic vessels; also known as the Haversian canal.

central chemoreceptor – one of the specialised receptors that are located in the brain that sense changes in hydrogen ion, oxygen, or carbon dioxide concentrations in the brain.

central nervous system (CNS) – anatomical division of the nervous system located within the cranial and vertebral cavities, namely the brain and spinal cord.

central sulcus – surface landmark of the cerebral cortex that marks the boundary between the frontal and parietal lobes.

central tolerance – B cell tolerance induced in immature B cells of the bone marrow.

central vein – vein that receives blood from hepatic sinusoids.

centriole – small, self-replicating organelle that provides the origin for microtubule growth and moves DNA during cell division.

centromere – region of attachment for two sister chromatids.

centrosome – cellular structure that organises microtubules during cell division.

cephalic flexure – curve in midbrain of the embryo that positions the forebrain ventrally.

cephalic phase – (also, reflex phase) initial phase of gastric secretion that occurs before food enters the stomach.

cephalic vein – superficial vessel in the upper arm; leads to the axillary vein.

cerebellum – region of the adult brain connected primarily to the pons that developed from the metencephalon (along with the pons) and is largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord.

cerebral aqueduct – connection of the ventricular system between the third and fourth ventricles located in the midbrain.

cerebral cortex – outermost layer of grey matter in the brain, where conscious perception takes place.

cerebral hemisphere – one half of the bilaterally symmetrical cerebrum.

cerebral peduncles – segments of the descending motor pathway that make up the white matter of the ventral midbrain.

cerebrospinal fluid (CSF) – circulatory medium within the CNS that is produced by ependymal cells in the choroid plexus filtering the blood.

cerebrovascular accident (CVA) – blockage of blood flow to the brain; also called a stroke.

cerebrum – region of the adult brain that develops from the telencephalon and is responsible for higher neurological functions such as memory, emotion, and consciousness.

cervical curve – posteriorly concave curvature of the cervical vertebral column region; a secondary curve of the vertebral column.

cervical enlargement – region of the ventral (anterior) horn of the spinal cord that has a larger population of motor neurons for the greater number of and finer control of muscles of the upper limb.

cervical plexus – nerve plexus associated with the upper cervical spinal nerves.

cervical vertebrae – seven vertebrae numbered as C1–C7 that are located in the neck region of the vertebral column.

cervix – elongate inferior end of the uterus where it connects to the vagina.

channel protein – membrane-spanning protein that has an inner pore which allows the passage of one or more substances.

chaperone – (also, chaperonin) protein that helps nascent protein in the folding process.

checkpoint – progress point in the cell cycle during which certain conditions must be met in order for the cell to proceed to a subsequence phase.

chemical digestion – enzymatic breakdown of food.

chemical synapse – connection between two neurons, or between a neuron and its target, where a neurotransmitter diffuses across a very short distance.

chemokine – soluble, long-range, cell-to-cell communication molecule.

chemoreceptor – sensory receptor cell that is sensitive to chemical stimuli, such as in taste, smell, or pain.

chief cell – gastric gland cell that secretes pepsinogen.

chief sensory nucleus – component of the trigeminal nuclei that is found in the pons.

chitin – type of carbohydrate that forms the outer skeleton of all arthropods that include crustaceans and insects; it also forms fungi cell walls.

chloride shift – facilitated diffusion that exchanges bicarbonate (HCO3–) with chloride (Cl–) ions.

cholinergic system – neurotransmitter system of acetylcholine, which includes its receptors and the enzyme acetylcholinesterase.

chondrocytes – cells of the cartilage.

chromatin – substance consisting of DNA and associated proteins.

chromosome – condensed version of chromatin.

chronic inflammation – inflammation occurring for long periods of time.

chordae tendineae – string-like extensions of tough connective tissue that extend from the flaps of the atrioventricular valves to the papillary muscles.

chorion – membrane that develops from the syncytiotrophoblast, cytotrophoblast, and mesoderm; surrounds the embryo and forms the foetal portion of the placenta through the chorionic villi.

chorionic membrane – precursor to the chorion; forms from extra-embryonic mesoderm cells.

chorionic villi – projections of the chorionic membrane that burrow into the endometrium and develop into the placenta.

choroid – highly vascular tissue in the wall of the eye that supplies the outer retina with blood/

choroid plexus – specialised structure containing ependymal cells that line blood capillaries and filter blood to produce CSF in the four ventricles of the brain.

chromaffin – neuroendocrine cells of the adrenal medulla.

chyle – lipid-rich lymph inside the lymphatic capillaries of the small intestine.

chylomicron – large lipid-transport compound made up of triglycerides, phospholipids, cholesterol, and proteins.

chyme – soupy liquid created when food is mixed with digestive secretions.

cilia – small appendage on certain cells formed by microtubules and modified for movement of materials across the cellular surface.

ciliary body – smooth muscle structure on the interior surface of the iris that controls the shape of the lens through the zonule fibres.

circadian rhythm – internal perception of the daily cycle of light and dark based on retinal activity related to sunlight.

circle of Willis – (also, arterial circle) anastomosis located at the base of the brain that ensures continual blood supply; formed from branches of the internal carotid and vertebral arteries; supplies blood to the brain.

circular folds – (also, plicae circulares) deep fold in the mucosa and submucosa of the small intestine.

circulatory shock – also simply called shock; a life-threatening medical condition in which the circulatory system is unable to supply enough blood flow to provide adequate oxygen and other nutrients to the tissues to maintain cellular metabolism.

circumduction – circular motion of the arm, thigh, hand, thumb, or finger that is produced by the sequential combination of flexion, abduction, extension, and adduction.

circumflex artery – branch of the left coronary artery that follows coronary sulcus.

cisterna chyli – bag-like vessel that forms the beginning of the thoracic duct.

class switching – ability of B cells to change the class of antibody they produce without altering the specificity for antigen.

clavicle – collarbone; elongated bone that articulates with the manubrium of the sternum medially and the acromion of the scapula laterally.

clavicular notch – paired notches located on the superior-lateral sides of the sternal manubrium, for articulation with the clavicle.

cleavage – form of mitotic cell division in which the cell divides but the total volume remains unchanged; this process serves to produce smaller and smaller cells.

cleavage furrow – contractile ring that forms around a cell during cytokinesis that pinches the cell into two halves.

clitoris – (also, glans clitoris) nerve-rich area of the vulva that contributes to sexual sensation during intercourse.

clonal anergy – process whereby B cells that react to soluble antigens in bone marrow are made non-functional.

clonal deletion – removal of self-reactive B cells by inducing apoptosis.

clonal expansion – growth of a clone of selected lymphocytes.

clonal selection – stimulating growth of lymphocytes that have specific receptors.

clone – group of lymphocytes sharing the same antigen receptor.

closed reduction – manual manipulation of a broken bone to set it into its natural position without surgery.

clotting – also called coagulation; complex process by which blood components form a plug to stop bleeding.

clotting factors – group of 12 identified substances active in coagulation.

coagulation – formation of a blood clot; part of the process of haemostasis.

coccyx – small bone located at inferior end of the adult vertebral column that is formed by the fusion of four coccygeal vertebrae; also referred to as the “tailbone”.

cochlea – auditory portion of the inner ear containing structures to transduce sound stimuli.

cochlear duct – space within the auditory portion of the inner ear that contains the organ of Corti and is adjacent to the scala tympani and scala vestibuli on either side.

codon – consecutive sequence of three nucleotides on an mRNA molecule that corresponds to a specific amino acid.

coeliac trunk – (also, coeliac artery) major branch of the abdominal aorta; gives rise to the left gastric artery, the splenic artery, and the common hepatic artery that forms the hepatic artery to the liver, the right gastric artery to the stomach, and the cystic artery to the gall bladder.

collagen fibres – flexible fibrous proteins that give connective tissue tensile strength.

colloid – viscous fluid in the central cavity of thyroid follicles, containing the glycoprotein thyroglobulin.

colon – part of the large intestine between the cecum and the rectum.

colony-stimulating factors (CSFs) – glycoproteins that trigger the proliferation and differentiation of myeloblasts into granular leukocytes (basophils, neutrophils, and eosinophils).

common bile duct – structure formed by the union of the common hepatic duct and the gallbladder’s cystic duct.

common carotid artery – right common carotid artery arises from the brachiocephalic artery, and the left common carotid arises from the aortic arch; gives rise to the external and internal carotid arteries; supplies the respective sides of the head and neck.

common hepatic artery – branch of the celiac trunk that forms the hepatic artery, the right gastric artery, and the cystic artery.

common hepatic duct – duct formed by the merger of the two hepatic ducts.

common iliac artery – branch of the aorta that leads to the internal and external iliac arteries.

common iliac vein – one of a pair of veins that flows into the inferior vena cava at the level of L5; the left common iliac vein drains the sacral region; divides into external and internal iliac veins near the inferior portion of the sacroiliac joint

common pathway – final coagulation pathway activated either by the intrinsic or the extrinsic pathway, and ending in the formation of a blood clot.

compact bone – dense osseous tissue that can withstand compressive forces.

complement – enzymatic cascade of constitutive blood proteins that have antipathogen effects, including the direct killing of bacteria.

compliance – degree to which a blood vessel can stretch as opposed to being rigid.

concentration gradient – difference in the concentration of a substance between two regions.

concentric contraction – muscle contraction that shortens the muscle to move a load.

conceptus – pre-implantation stage of a fertilised egg and its associated membran.

conducting zone – region of the respiratory system that includes the organs and structures that provide passageways for air and are not directly involved in gas exchange.

condylar process of the mandible – thickened upward projection from posterior margin of mandibular ramus.

condyle – oval-shaped process located at the top of the condylar process of the mandible.

condyloid joint – synovial joint in which the shallow depression at the end of one bone receives a rounded end from a second bone or a rounded structure formed by two bones; found at the metacarpophalangeal joints of the fingers or the radiocarpal joint of the wrist; functionally classified as a biaxial joint.

cone photoreceptor – one of the two types of retinal receptor cell that is specialised for colour vision through the use of three photopigments distributed through three separate populations of cells.

connective tissue – type of tissue that serves to hold in place, connect, and integrate the body’s organs and systems.

connective tissue membrane – connective tissue that encapsulates organs and lines movable joints.

connective tissue proper – connective tissue containing a viscous matrix, fibres, and cells.

constant region domain – part of a lymphocyte antigen receptor that does not vary much between different receptor types.

continuous capillary – most common type of capillary, found in virtually all tissues except epithelia and cartilage; contains very small gaps in the endothelial lining that permit exchange.

continuous conduction – slow propagation of an action potential along an unmyelinated axon owing to voltage-gated Na+ channels located along the entire length of the cell membrane.

contractility – ability to shorten (contract) forcibly.

contraction phase – twitch contraction phase when tension increases.

contralateral – word meaning “on the opposite side,” as in axons that cross the midline in a fibre tract.

control centre – compares values to their normal range; deviations cause the activation of an effector.

coracoclavicular ligament – strong band of connective tissue that anchors the coracoid process of the scapula to the lateral clavicle; provides important indirect support for the acromioclavicular joint.

coracohumeral ligament – intrinsic ligament of the shoulder joint; runs from the coracoid process of the scapula to the anterior humerus.

coracoid process – short, hook-like process that projects anteriorly and laterally from the superior margin of the scapula.

corn – type of callus that is named for its shape and the elliptical motion of the abrasive force.

cornea – fibrous covering of the anterior region of the eye that is transparent so that light can pass through it.

corneal reflex – protective response to stimulation of the cornea causing contraction of the orbicularis oculi muscle resulting in blinking of the eye.

corona radiata – in an oocyte, a layer of granulosa cells that surrounds the oocyte and that must be penetrated by sperm before fertilisation can occur.

coronal suture – joint that unites the frontal bone to the right and left parietal bones across the top of the skull.

coronary arteries – branches of the ascending aorta that supply blood to the heart; the left coronary artery feeds the left side of the heart, the left atrium and ventricle, and the interventricular septum; the right coronary artery feeds the right atrium, portions of both ventricles, and the heart conduction system.

coronary sinus – large, thin-walled vein on the posterior surface of the heart that lies within the atrioventricular sulcus and drains the heart myocardium directly into the right atrium.

coronary sulcus – sulcus that marks the boundary between the atria and ventricles.

coronary veins – vessels that drain the heart and generally parallel the large surface arteries.

coronoid fossa – depression on the anterior surface of the humerus above the trochlea; this space receives the coronoid process of the ulna when the elbow is maximally flexed.

coronoid process of the mandible – flattened upward projection from the anterior margin of the mandibular ramus.

coronoid process of the ulna – projecting bony lip located on the anterior, proximal ulna; forms the inferior margin of the trochlear notch.

corpus albicans – non-functional structure remaining in the ovarian stroma following structural and functional regression of the corpus luteum.

corpus callosum – large white matter structure that connects the right and left cerebral hemispheres.

corpus cavernosum – either of two columns of erectile tissue in the penis that fill with blood during an erection.

corpus luteum – transformed follicle after ovulation that secretes progesterone.

corpus spongiosum – (plural = corpora cavernosa) column of erectile tissue in the penis that fills with blood during an erection and surrounds the penile urethra on the ventral portion of the penis.

cortical nephrons – nephrons with loops of Henle that do not extend into the renal medulla.

cortical reaction – following fertilisation, the release of cortical granules from the oocyte’s plasma membrane into the zona pellucida creating a fertilisation membrane that prevents any further attachment or penetration of sperm; part of the slow block to polyspermy.

cortex – in hair, the second or middle layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb.

corticobulbar tract – connection between the cortex and the brain stem responsible for generating movement.

corticospinal tract – connection between the cortex and the spinal cord responsible for generating movement.

cortisol – glucocorticoid important in gluconeogenesis, the catabolism of glycogen, and downregulation of the immune system.

costal cartilage – hyaline cartilage structure attached to the anterior end of each rib that provides for either direct or indirect attachment of most ribs to the sternum.

costal facet – site on the lateral sides of a thoracic vertebra for articulation with the head of a rib.

costal groove – shallow groove along the inferior margin of a rib that provides passage for blood vessels and a nerve.

costoclavicular ligament – band of connective tissue that unites the medial clavicle with the first rib.

coxal bone – hip bone.

cranial – describes a position above or higher than another part of the body proper; also referred to as superior.

cranial cavity – division of the posterior (dorsal) cavity that houses the brain.

cranial nerve – one of twelve nerves connected to the brain that are responsible for sensory or motor functions of the head and neck.

cranial nerve ganglion – sensory ganglion of cranial nerves.

cranium – skull.

creatine phosphate – phosphagen used to store energy from ATP and transfer it to muscle.

cribriform plate – small, flattened areas with numerous small openings, located to either side of the midline in the floor of the anterior cranial fossa; formed by the ethmoid bone.

cricoid cartilage – portion of the larynx composed of a ring of cartilage with a wide posterior region and a thinner anterior region; attached to the oesophagus.

crista galli – small upward projection located at the midline in the floor of the anterior cranial fossa; formed by the ethmoid bone.

cross-matching – blood test for determination of compatibility between donor RBC and patient’s plasma.

counter current multiplier system – involves the descending and ascending loops of Henle directing forming urine in opposing directions to create a concentration gradient when combined with variable permeability and sodium pumping.

crown – portion of tooth visible superior to the gum line.

cuboid – tarsal bone that articulates posteriorly with the calcaneus bone, medially with the lateral cuneiform bone, and anteriorly with the fourth and fifth metatarsal bones.

cupula – specialised structure within the base of a semicircular canal that bends the stereocilia of hair cells when the head rotates by way of the relative movement of the enclosed fluid.

cuspid – (also, canine) pointed tooth used for tearing and shredding food.

cutaneous membrane – skin; epithelial tissue made up of a stratified squamous epithelial cells that cover the outside of the body.

cuticle – in hair, the outermost layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb.

cyclic adenosine monophosphate (cAMP) – second messenger that, in response to adenylyl cyclase activation, triggers a phosphorylation cascade.

cyclin – one of a group of proteins that function in the progression of the cell cycle.

cyclin-dependent kinase (CDK) – one of a group of enzymes associated with cyclins that help them perform their functions.

cystic artery – branch of the common hepatic artery; supplies blood to the gall bladder.

cystic duct – duct through which bile drains and enters the gallbladder.

cytokine – soluble, short-range, cell-to-cell communication molecule.

cytokines – class of proteins that act as autocrine or paracrine signalling molecules; in the cardiovascular system, they stimulate the proliferation of progenitor cells and help to stimulate both nonspecific and specific resistance to disease.

cytokinesis – final stage in cell division, where the cytoplasm divides to form two separate daughter cells.

cytoplasm – internal material between the cell membrane and nucleus of a cell, mainly consisting of a water-based fluid called cytosol, within which are all the other organelles and cellular solute and suspended materials.

cytoskeleton – “skeleton” of a cell; formed by rod-like proteins that support the cell’s shape and provide, among other functions, locomotive abilities.

cytosol – clear, semi-fluid medium of the cytoplasm, made up mostly of water.

cytotoxic T cells (Tc) – T lymphocytes with the ability to induce apoptosis in target cells.

D

Dalton’s law – statement of the principle that a specific gas type in a mixture exerts its own pressure, as if that specific gas type was not part of a mixture of gases.

deciduous tooth – one of 20 “baby teeth”.

decussate – to cross the midline, as in fibres that project from one side of the body to the other.

deep – describes a position farther from the surface of the body.

deep femoral artery – branch of the femoral artery; gives rise to the lateral circumflex arteries.

deep femoral vein – drains blood from the deeper portions of the thigh and leads to the femoral vein.

defaecation – elimination of undigested substances from the body in the form of faeces.

defensins – antimicrobial proteins released from neutrophils and macrophages that create openings in the plasma membranes to kill cells.

deglutition – three-stage process of swallowing.

dehydration – state of containing insufficient water in blood and other tissues.

dehydration synthesis – (also, condensation) reaction that links monomer molecules, releasing a water molecule for each bond formed..

delayed hypersensitivity – (type IV) T cell-mediated immune response against pathogens infiltrating interstitial tissues, causing cellular infiltrate.

delta cell – minor cell type in the pancreas that secretes the hormone somatostatin.

deltoid ligament – broad intrinsic ligament located on the medial side of the ankle joint; supports the talus at the talocrural joint and resists excess eversion of the foot.

deltoid tuberosity – roughened, V-shaped region located laterally on the mid-shaft of the humerus.

denaturation – loss of shape in a protein as a result of changes in temperature, pH, or chemical exposure.

dendrite – one of many branchlike processes that extends from the neuron cell body and functions as a contact for incoming signals (synapses) from other neurons or sensory cells.

dens – bony projection (odontoid process) that extends upward from the body of the C2 (axis) vertebra.

dens – tooth.

dense body – sarcoplasmic structure that attaches to the sarcolemma and shortens the muscle as thin filaments slide past thick filaments.

dense connective tissue – connective tissue proper that contains many fibres that provide both elasticity and protection.

dentin – bone-like tissue immediately deep to the enamel of the crown or cementum of the root of a tooth.

dentition – set of teeth.

deoxyhemoglobin – molecule of haemoglobin without an oxygen molecule bound to it.

deoxyribonuclease – pancreatic enzyme that digests DNA.

deoxyribonucleic acid (DNA) – double-helical molecule that carries the cell’s hereditary information.

depolarise – to reduce the voltage difference between the inside and outside of a cell’s plasma membrane (the sarcolemma for a muscle fibre), making the inside less negative than at rest.

depolarisation – change in a cell membrane potential from rest toward zero.

depression – downward (inferior) motion of the scapula or mandible.

dermal papilla – (plural = dermal papillae) extension of the papillary layer of the dermis that increases surface contact between the epidermis and dermis.

dermis – layer of skin between the epidermis and hypodermis, composed mainly of connective tissue and containing blood vessels, hair follicles, sweat glands, and other structures.

descending aorta – portion of the aorta that continues downward past the end of the aortic arch; subdivided into the thoracic aorta and the abdominal aorta.

descending colon – part of the colon between the transverse colon and the sigmoid colon.

descending tract – central nervous system fibres carrying motor commands from the brain to the spinal cord or periphery.

desmosome – structure that forms an impermeable junction between cells.

detrusor muscle – smooth muscle in the bladder wall; fibres run in all directions to reduce the size of the organ when emptying it of urine.

diacylglycerol (DAG) – molecule that, like cAMP, activates protein kinases, thereby initiating a phosphorylation cascade.

diapedesis – (also, emigration) process by which leukocytes squeeze through adjacent cells in a blood vessel wall to enter tissues.

diaphysis – tubular shaft that runs between the proximal and distal ends of a long bone.

diarthrosis – freely mobile joint.

diastole – period of time when the heart muscle is relaxed and the chambers fill with blood.

diastolic pressure – lower number recorded when measuring arterial blood pressure; represents the minimal value corresponding to the pressure that remains during ventricular relaxation.

diabetes mellitus – condition caused by destruction or dysfunction of the beta cells of the pancreas or cellular resistance to insulin that results in abnormally high blood glucose levels.

diencephalon – region of the adult brain that retains its name from embryonic development and includes the thalamus and hypothalamus.

diffusion – movement of a substance from an area of higher concentration to one of lower concentration.

digital arteries – formed from the superficial and deep palmar arches; supply blood to the digits.

digital veins – drain the digits and feed into the palmar arches of the hand and dorsal venous arch of the foot.

dihydroxyvitamin D – active form of vitamin D required by the intestinal epithelial cells for the absorption of calcium.

dipeptidase – brush border enzyme that acts on proteins.

diploë – layer of spongy bone, that is sandwiched between two the layers of compact bone found in flat bones.

diploid – condition marked by the presence of a double complement of genetic material (two sets of chromosomes, one set inherited from each of two parents).

direct pathway – connections within the basal nuclei from the striatum to the globus pallidus internal segment and substantia nigra pars reticulata that disinhibit the thalamus to increase cortical control of movement.

disaccharide – two sugar monomers that a glycosidic bond links.

disinhibition – disynaptic connection in which the first synapse inhibits the second cell, which then stops inhibiting the final target.

distal – describes a position farther from the point of attachment or the trunk of the body.

distal convoluted tubules – portions of the nephron distal to the loop of Henle that receive hyposmotic filtrate from the loop of Henle and empty into collecting ducts.

distal radioulnar joint – articulation between the head of the ulna and the ulnar notch of the radius.

distal tibiofibular joint – articulation between the distal fibula and the fibular notch of the tibia.

diuresis – excess production of urine.

diuretic – compound that increases urine output, leading to decreased water conservation.

DNA polymerase – enzyme that functions in adding new nucleotides to a growing strand of DNA during DNA replication.

DNA replication – process of duplicating a molecule of DNA.

dorsal – describes the back or direction toward the back of the body; also referred to as posterior.

dorsal arch – (also, arcuate arch) formed from the anastomosis of the dorsalis pedis artery and medial and plantar arteries; branches supply the distal portions of the foot and digits.

dorsal cavity – posterior body cavity that houses the brain and spinal cord; also referred to the posterior body cavity.

dorsal column system – ascending tract of the spinal cord associated with fine touch and proprioceptive sensations.

dorsal (posterior) nerve root – axons entering the posterior horn of the spinal cord.

dorsal respiratory group (DRG) – region of the medulla oblongata that stimulates the contraction of the diaphragm and intercostal muscles to induce inspiration.

dorsal (posterior) root ganglion – sensory ganglion attached to the posterior nerve root of a spinal nerve.

dorsal stream – connections between cortical areas from the occipital to parietal lobes that are responsible for the perception of visual motion and guiding movement of the body in relation to that motion.

dorsalis pedis artery – forms from the anterior tibial artery; branches repeatedly to supply blood to the tarsal and dorsal regions of the foot.

dorsal venous arch – drains blood from digital veins and vessels on the superior surface of the foot.

dorsiflexion – movement at the ankle that brings the top of the foot toward the anterior leg.

dorsum nasi – intermediate portion of the external nose that connects the bridge to the apex and is supported by the nasal bone.

downregulation – decrease in the number of hormone receptors, typically in response to chronically excessive levels of a hormone.

ductus arteriosus – shunt in the foetal pulmonary trunk that diverts oxygenated blood back to the aorta.

ductus deferens – (also, vas deferens) duct that transports sperm from the epididymis through the spermatic cord and into the ejaculatory duct; also referred as the vas deferens.

ductus venosus – shunt that causes oxygenated blood to bypass the foetal liver on its way to the inferior vena cava.

duodenal gland – (also, Brunner’s gland) mucous-secreting gland in the duodenal submucosa.

duodenum – first part of the small intestine, which starts at the pyloric sphincter and ends at the jejunum.

dura mater – tough, fibrous, outer layer of the meninges that is attached to the inner surface of the cranium and vertebral column and surrounds the entire CNS.

dural sinus – any of the venous structures surrounding the brain, enclosed within the dura mater, which drain blood from the CNS to the common venous return of the jugular veins.

E

early induced immune response – includes antimicrobial proteins stimulated during the first several days of an infection.

ear ossicles – three small bones located in the middle ear cavity that serve to transmit sound vibrations to the inner ear.

eccentric contraction – muscle contraction that lengthens the muscle as the tension is diminished.

eccrine sweat gland – type of sweat gland that is common throughout the skin surface; it produces a hypotonic sweat for thermoregulation.

ectoderm – outermost embryonic germ layer from which the epidermis and the nervous tissue derive.

ectopic pregnancy – implantation of an embryo outside of the uterus.

eczema – skin condition due to an allergic reaction, which resembles a rash.

effector – organ that can cause a change in a value.

efferent lymphatic vessels – lead out of a lymph node.

effector protein – enzyme that catalyses the generation of a new molecule, which acts as the intracellular mediator of the signal that binds to the receptor.

effector T cells – immune cells with a direct, adverse effect on a pathogen.

efferent arteriole – arteriole carrying blood from the glomerulus to the capillary beds around the convoluted tubules and loop of Henle; portion of the portal system.

ejaculatory duct – duct that connects the ampulla of the ductus deferens with the duct of the seminal vesicle at the prostatic urethra.

ejection fraction – portion of the blood that is pumped or ejected from the heart with each contraction; mathematically represented by SV divided by EDV.

elastic artery – (also, conducting artery) artery with abundant elastic fibres located closer to the heart, which maintains the pressure gradient and conducts blood to smaller branches.

elastic cartilage – type of cartilage, with elastin as the major protein, characterised by rigid support as well as elasticity

elastic fibres – fibrous protein within connective tissue that contains a high percentage of the protein elastin that allows the fibres to stretch and return to original size.

elasticity – ability to stretch and rebound.

elbow joint – joint located between the upper arm and forearm regions of the upper limb; formed by the articulations between the trochlea of the humerus and the trochlear notch of the ulna, and the capitulum of the humerus and the head of the radius.

electrical gradient – difference in the electrical charge (potential) between two regions.

electrical synapse – connection between two neurons, or any two electrically active cells, where ions flow directly through channels spanning their adjacent cell membranes.

electrocardiogram (ECG) – surface recording of the electrical activity of the heart that can be used for diagnosis of irregular heart function; also abbreviated as EKG.

electrochemical exclusion – principle of selectively allowing ions through a channel on the basis of their charge.

eleidin – clear protein-bound lipid found in the stratum lucidum that is derived from keratohyalin and helps to prevent water loss.

elevation – upward (superior) motion of the scapula or mandible.

embolus – thrombus that has broken free from the blood vessel wall and entered the circulation.

emigration – (also, diapedesis) process by which leukocytes squeeze through adjacent cells in a blood vessel wall to enter tissues.

embryo – developing human during weeks 3–8.

embryonic folding – process by which an embryo develops from a flat disc of cells to a three-dimensional shape resembling a cylinder.

enamel – covering of the dentin of the crown of a tooth.

encapsulated ending – configuration of a sensory receptor neuron with dendrites surrounded by specialised structures to aid in transduction of a particular type of sensation, such as the lamellated corpuscles in the deep dermis and subcutaneous tissue.

end diastolic volume (EDV) – (also, preload) the amount of blood in the ventricles at the end of atrial systole just prior to ventricular contraction.

endocardial tubes – stage in which lumens form within the expanding cardiogenic cords, forming hollow structures.

endocardium – innermost layer of the heart lining the heart chambers and heart valves; composed of endothelium reinforced with a thin layer of connective tissue that binds to the myocardium.

endochondral ossification – process in which bone forms by replacing hyaline cartilage.

endocrine gland – groups of cells that release chemical signals into the intercellular fluid to be picked up and transported to their target organs by blood.

endocrine system – cells, tissues, and organs that secrete hormones as a primary or secondary function and play an integral role in normal bodily processes.

endocytosis – import of material into the cell by formation of a membrane-bound vesicle.

endoderm – innermost embryonic germ layer from which most of the digestive system and lower respiratory system derive.

endometrium – inner lining of the uterus, part of which builds up during the secretory phase of the menstrual cycle and then sheds with menses.

endomysium – loose, and well-hydrated connective tissue covering each muscle fibre in a skeletal muscle.

endoneurium – innermost layer of connective tissue that surrounds individual axons within a nerve.

endoplasmic reticulum (ER) – cellular organelle that consists of interconnected membrane-bound tubules, which may or may not be associated with ribosomes (rough type or smooth type, respectively).

endosteum – delicate membranous lining of a bone’s medullary cavity.

end systolic volume (ESV) – amount of blood remaining in each ventricle following systole.

endothelins – group of vasoconstrictive, 21-amino acid peptides; produced by endothelial cells of the renal blood vessels, mesangial cells, and cells of the DCT.

endothelium – tissue that lines vessels of the lymphatic and cardiovascular system, made up of a simple squamous epithelium.

enteric nervous system (ENS) – neural tissue associated with the digestive system that is responsible for nervous control through autonomic connections.

enteric plexus – neuronal plexus in the wall of the intestines, which is part of the enteric nervous system.

enteroendocrine cell – gastric gland cell that releases hormones.

enterohepatic circulation – recycling mechanism that conserves bile salts.

enteropeptidase – intestinal brush-border enzyme that activates trypsinogen to trypsin.

enzyme – catalyst in a biochemical reaction that is usually a complex or conjugated protein.

eosinophils – granulocytes that stain with eosin; they release antihistamines and are especially active against parasitic worms.

ependymal cell – glial cell type in the CNS responsible for producing cerebrospinal fluid.

epiblast – upper layer of cells of the embryonic disc that forms from the inner cell mass; gives rise to all three germ layers.

epicardial coronary arteries – surface arteries of the heart that generally follow the sulci.

epicardium – innermost layer of the serous pericardium and the outermost layer of the heart wall.

epidermis – outermost tissue layer of the skin.

epididymis – (plural = epididymides) coiled tubular structure in which sperm start to mature and are stored until ejaculation.

epiglottis – leaf-shaped piece of elastic cartilage that is a portion of the larynx that swings to close the trachea during swallowing.

epimysium – outer layer of connective tissue around a skeletal muscle.

epineurium – outermost layer of connective tissue that surrounds an entire nerve.

epiphyseal line – completely ossified remnant of the epiphyseal plate.

epiphyseal plate – (also, growth plate) sheet of hyaline cartilage in the metaphysis of an immature bone; replaced by bone tissue as the organ grows in length.

epiphysis – wide section at each end of a long bone; filled with spongy bone and red marrow.

epiploic appendage – small sac of fat-filled visceral peritoneum attached to teniae coli.

epithalamus – region of the diecephalon containing the pineal gland.

epithelial membrane – epithelium attached to a layer of connective tissue.

epithelial tissue – type of tissue that serves primarily as a covering or lining of body parts, protecting the body; it also functions in absorption, transport, and secretion.

eponychium – nail fold that meets the proximal end of the nail body, also called the cuticle.

epsilon cell – minor cell type in the pancreas that secretes the hormone ghrelin.

equilibrium – sense of balance that includes sensations of position and movement of the head.

erythroblastosis fetalis – disease of Rh factor-positive newborns in Rh-negative mothers with multiple Rh-positive children; resulting from the action of maternal antibodies against foetal blood.

erythrocyte – (also, red blood cell) mature myeloid blood cell that is composed mostly of haemoglobin and functions primarily in the transportation of oxygen and carbon dioxide.

erythropoietin (EPO) – glycoprotein that triggers the bone marrow to produce haemoglobin and RBCs; secreted by the kidney in response to low oxygen levels.

ethmoid air cell – one of several small, air-filled spaces located within the lateral sides of the ethmoid bone, between the orbit and upper nasal cavity.

ethmoid bone – unpaired bone that forms the roof and upper, lateral walls of the nasal cavity, portions of the floor of the anterior cranial fossa and medial wall of orbit, and the upper portion of the nasal septum.

eversion – foot movement involving the intertarsal joints of the foot in which the bottom of the foot is turned laterally, away from the midline.

excitability – ability to undergo neural stimulation.

excitable membrane – cell membrane that regulates the movement of ions so that an electrical signal can be generated.

excitation-contraction coupling – sequence of events from motor neuron signalling to a skeletal muscle fibre to contraction of the fibre’s sarcomeres.

excitatory postsynaptic potential (EPSP) – graded potential in the postsynaptic membrane that is the result of depolarisation and makes an action potential more likely to occur.

executive functions – cognitive processes of the prefrontal cortex that lead to directing goal-directed behaviour, which is a precursor to executing motor commands.

exocrine gland – group of epithelial cells that secrete substances through ducts that open to the skin or to internal body surfaces that lead to the exterior of the body.

exocrine system – cells, tissues, and organs that secrete substances directly to target tissues via glandular ducts.

exocytosis – export of a substance out of a cell by formation of a membrane-bound vesicle.

exon – one of the coding regions of an mRNA molecule that remain after splicing.

expiration – (also, exhalation) process that causes the air to leave the lungs.

expiratory reserve volume (ERV) – amount of air that can be forcefully exhaled after a normal tidal exhalation.

extensibility – ability to lengthen (extend).

extension – movement in the sagittal plane that increases the angle of a joint (straightens the joint); motion involving posterior bending of the vertebral column or returning to the upright position from a flexed position.

external acoustic meatus – ear canal opening located on the lateral side of the skull.

external anal sphincter – voluntary skeletal muscle sphincter in the anal canal.

external callus – collar of hyaline cartilage and bone that forms around the outside of a fracture.

external carotid artery – arises from the common carotid artery; supplies blood to numerous structures within the face, lower jaw, neck, oesophagus, and larynx.

external ear – structures on the lateral surface of the head, including the auricle and the ear canal back to the tympanic membrane.

external elastic membrane – membrane composed of elastic fibres that separates the tunica media from the tunica externa; seen in larger arteries.

external iliac artery – branch of the common iliac artery that leaves the body cavity and becomes a femoral artery; supplies blood to the lower limbs.

external iliac vein – formed when the femoral vein passes into the body cavity; drains the legs and leads to the common iliac vein.

external jugular vein – one of a pair of major veins located in the superficial neck region that drains blood from the more superficial portions of the head, scalp, and cranial regions, and leads to the subclavian vein.

external nose – region of the nose that is easily visible to others.

external occipital protuberance – small bump located at the midline on the posterior skull.

external respiration – gas exchange that occurs in the alveoli.

external root sheath – outer layer of the hair follicle that is an extension of the epidermis, which encloses the hair root.

external urinary sphincter – skeletal muscle; must be relaxed consciously to void urine.

exteroceptor – sensory receptor that is positioned to interpret stimuli from the external environment, such as photoreceptors in the eye or somatosensory receptors in the skin.

extracellular fluid (ECF) – fluid exterior to cells; includes the interstitial fluid, blood plasma, and fluid found in other reservoirs in the body.

extraocular muscles – six skeletal muscles that control eye movement within the orbit.

extrapyramidal system – pathways between the brain and spinal cord that are separate from the corticospinal tract and are responsible for modulating the movements generated through that primary pathway.

extrinsic ligament – ligament located outside of the articular capsule of a synovial joint.

extrinsic pathway – initial coagulation pathway that begins with tissue damage and results in the activation of the common pathway.

F

facet – small, flattened area on a bone for an articulation (joint) with another bone, or for muscle attachment.

facial bones – fourteen bones that support the facial structures and form the upper and lower jaws and the hard palate.

facial nerve – seventh cranial nerve; responsible for contraction of the facial muscles and for part of the sense of taste, as well as causing saliva production.

facilitated diffusion – diffusion of a substance with the aid of a membrane protein.

faeces – semisolid waste product of digestion.

false ribs – vertebrochondral ribs 8–12 whose costal cartilage either attaches indirectly to the sternum via the costal cartilage of the next higher rib or does not attach to the sternum at all.

fascicle – bundle of muscle fibres within a skeletal muscle.

fasciculus cuneatus – lateral division of the dorsal column system composed of fibres from sensory neurons in the upper body.

fasciculus gracilis – medial division of the dorsal column system composed of fibres from sensory neurons in the lower body.

fas ligand – molecule expressed on cytotoxic T cells and NK cells that binds to the fas molecule on a target cell and induces it do undergo apoptosis.

fast glycolytic (FG) – muscle fibre that primarily uses anaerobic glycolysis.

fast oxidative (FO) – intermediate muscle fibre that is between slow oxidative and fast glycolytic fibres.

fauces – portion of the posterior oral cavity that connects the oral cavity to the oropharynx.

Fc region – in an antibody molecule, the site where the two termini of the heavy chains come together; many cells have receptors for this portion of the antibody, adding functionality to these molecules.

femoral artery – continuation of the external iliac artery after it passes through the body cavity; divides into several smaller branches, the lateral deep femoral artery, and the genicular artery; becomes the popliteal artery as it passes posterior to the knee.

femoral circumflex vein – forms a loop around the femur just inferior to the trochanters; drains blood from the areas around the head and neck of the femur; leads to the femoral vein.

femoral nerve – systemic nerve of the anterior leg that arises from the lumbar plexus.

femoral vein – drains the upper leg; receives blood from the great saphenous vein, the deep femoral vein, and the femoral circumflex vein; becomes the external iliac vein when it crosses the body wall.

femoropatellar joint – portion of the knee joint consisting of the articulation between the distal femur and the patella.

femur – thigh bone; the single bone of the thigh.

fenestrated capillary – type of capillary with pores or fenestrations in the endothelium that allow for rapid passage of certain small materials.

fenestrations – small windows through a cell, allowing rapid filtration based on size; formed in such a way as to allow substances to cross through a cell without mixing with cell contents.

ferritin – protein-containing storage form of iron found in the bone marrow, liver, and spleen.

fertilisation – unification of genetic material from male and female haploid gametes.

fertilisation membrane – impenetrable barrier that coats a nascent zygote; part of the slow block to polyspermy.

fibrin – insoluble, filamentous protein that forms the structure of a blood clot.

fibrinogen – plasma protein produced in the liver and involved in blood clotting.

fibrinolysis – gradual degradation of a blood clot.

fibrocyte – less active form of fibroblast.

fibroelastic membrane – specialised membrane that connects the ends of the C-shape cartilage in the trachea; contains smooth muscle fibres.

fibrosis – replacement of muscle fibres by scar tissue.

fibrous joint – joint where the articulating areas of the adjacent bones are connected by fibrous connective tissue.

fibrous tunic – outer layer of the eye primarily composed of connective tissue known as the sclera and cornea.

fibula – thin, non-weight-bearing bone found on the lateral side of the leg.

fibular collateral ligament – extrinsic ligament of the knee joint that spans from the lateral epicondyle of the femur to the head of the fibula; resists hyperextension and rotation of the extended knee.

fibular nerve – systemic nerve of the posterior leg that begins as part of the sciatic nerve.

fibular notch – wide groove on the lateral side of the distal tibia for articulation with the fibula at the distal tibiofibular joint.

fibular vein – drains the muscles and integument near the fibula and leads to the popliteal vein.

filling time – duration of ventricular diastole during which filling occurs.

filtration – in the cardiovascular system, the movement of material from a capillary into the interstitial fluid, moving from an area of higher pressure to lower pressure.

fimbriae – finger-like projections on the distal uterine tubes.

first messenger – hormone that binds to a cell membrane hormone receptor and triggers activation of a second messenger system.

filtration slits – formed by pedicels of podocytes; substances filter between the pedicels based on size.

flagellum – appendage on certain cells formed by microtubules and modified for movement.

flat bone – thin and curved bone; serves as a point of attachment for muscles and protects internal organs.

flatus – gas in the intestine.

flexion – movement in the sagittal plane that decreases the angle of a joint (bends the joint); motion involving anterior bending of the vertebral column.

flexor retinaculum – strong band of connective tissue at the anterior wrist that spans the top of the U-shaped grouping of the carpal bones to form the roof of the carpal tunnel.

floating ribs – vertebral ribs 11–12 that do not attach to the sternum or to the costal cartilage of another rib.

fluid compartment – fluid inside all cells of the body constitutes a compartment system that is largely segregated from other systems.

fluid connective tissue – specialised cells that circulate in a watery fluid containing salts, nutrients, and dissolved proteins.

foetus – developing human during the time from the end of the embryonic period (week 9) to birth.

follicle – ovarian structure of one oocyte and surrounding granulosa (and later theca) cells.

follicle-stimulating hormone (FSH) – anterior pituitary hormone that stimulates the production and maturation of sex cells.

folliculogenesis – development of ovarian follicles from primordial to tertiary under the stimulation of gonadotropins.

fontanelle – expanded area of fibrous connective tissue that separates the brain-case bones of the skull prior to birth and during the first year after birth.

foot – portion of the lower limb located distal to the ankle joint.

foramen lacerum – irregular opening in the base of the skull, located inferior to the exit of carotid canal.

foramen magnum – large opening in the occipital bone of the skull through which the spinal cord emerges and the vertebral arteries enter the cranium.

foramen ovale – opening in the foetal heart that allows blood to flow directly from the right atrium to the left atrium, bypassing the foetal pulmonary circuit.

foramen ovale of the middle cranial fossa – oval-shaped opening in the floor of the middle cranial fossa.

foramen rotundum – round opening in the floor of the middle cranial fossa, located between the superior orbital fissure and foramen ovale.

foramen spinosum – small opening in the floor of the middle cranial fossa, located lateral to the foramen ovale.

forced breathing – (also, hyperpnoea) mode of breathing that occurs during exercise or by active thought that requires muscle contraction for both inspiration and expiration.

forearm – region of the upper limb located between the elbow and wrist joints; contains the radius and ulna bones.

forebrain – anterior region of the adult brain that develops from the prosencephalon and includes the cerebrum and diencephalon.

foregut – endoderm of the embryo towards the head region.

forming urine – filtrate undergoing modifications through secretion and reabsorption before true urine is produced.

fossa – (plural = fossae) shallow depression on the surface of a bone.

fossa ovalis – oval-shaped depression in the interatrial septum that marks the former location of the foramen ovale.

fourth ventricle – the portion of the ventricular system that is in the region of the brain stem and opens into the subarachnoid space through the median and lateral apertures.

fovea – exact centre of the retina at which visual stimuli are focused for maximal acuity, where the retina is thinnest, at which there is nothing but photoreceptors.

fovea capitis – minor indentation on the head of the femur that serves as the site of attachment for the ligament to the head of the femur.

fracture – broken bone.

fracture haematoma – blood clot that forms at the site of a broken bone.

Frank-Starling mechanism – relationship between ventricular stretch and contraction in which the force of heart contraction is directly proportional to the initial length of the muscle fibre.

free nerve ending – configuration of a sensory receptor neuron with dendrites in the connective tissue of the organ, such as in the dermis of the skin, that are most often sensitive to chemical, thermal, and mechanical stimuli.

frontal bone – unpaired bone that forms forehead, roof of orbit, and floor of anterior cranial fossa.

frontal eye field – region of the frontal lobe associated with motor commands to orient the eyes toward an object of visual attention.

frontal lobe – region of the cerebral cortex directly beneath the frontal bone of the cranium.

frontal plane – two-dimensional, vertical plane that divides the body or organ into anterior and posterior portions.

frontal sinus – air-filled space within the frontal bone; most anterior of the paranasal sinuses.

full thickness burns – burn that penetrates and destroys the full thickness of the skin (epidermis and dermis).

functional residual capacity (FRC) – sum of ERV and RV, which is the amount of air that remains in the lungs after a tidal expiration.

fundus – dome-shaped region of the stomach above and to the left of the cardia.

fundus – (of the uterus) domed portion of the uterus that is superior to the uterine tubes.

G

G cell – gastrin-secreting enteroendocrine cell.

gallbladder – accessory digestive organ that stores and concentrates bile.

gamete – haploid reproductive cell that contributes genetic material to form an offspring.

gamma cell (PP cell) – minor cell type in the pancreas that secretes the hormone pancreatic polypeptide.

ganglion – localised collection of neuron cell bodies in the peripheral nervous system.

gap junction – allows cytoplasmic communications to occur between cells.

gastric emptying – process by which mixing waves gradually cause the release of chyme into the duodenum.

gastric gland – gland in the stomach mucosal epithelium that produces gastric juice.

gastric phase – phase of gastric secretion that begins when food enters the stomach.

gastric pit – narrow channel formed by the epithelial lining of the stomach mucosa.

gastric plexuses – neuronal networks in the wall of the stomach that are part of the enteric nervous system.

gastrin – peptide hormone that stimulates secretion of hydrochloric acid and gut motility.

gastrocolic reflex – propulsive movement in the colon activated by the presence of food in the stomach.

gastroileal reflex – long reflex that increases the strength of segmentation in the ileum.

gastrointestinal microbiota –  collection of microorganisms in the gastrointestinal tract.

gastrointestinal tract (alimentary canal) – continuous muscular digestive tube that extends from the mouth to the anus.

gastrulation – process of cell migration and differentiation into three primary germ layers following cleavage and implantation.

gated – property of a channel that determines how it opens under specific conditions, such as voltage change or physical deformation.

glassy membrane – layer of connective tissue that surrounds the base of the hair follicle, connecting it to the dermis.

gene – functional length of DNA that provides the genetic information necessary to build a protein.

gene expression – active interpretation of the information coded in a gene to produce a functional gene product.

general adaptation syndrome (GAS) – the human body’s three-stage response pattern to short- and long-term stress.

general sense – any sensory system that is distributed throughout the body and incorporated into organs of multiple other systems, such as the walls of the digestive organs or the skin.

generator potential – graded potential from dendrites of a unipolar cell which generates the action potential in the initial segment of that cell’s axon.

genicular artery – branch of the femoral artery; supplies blood to the region of the knee.

genome – entire complement of an organism’s DNA; found within virtually every cell.

germinal centres – clusters of rapidly proliferating B cells found in secondary lymphoid tissues.

gestation – in human development, the period required for embryonic and foetal development in utero; pregnancy.

gigantism – disorder in children caused when abnormally high levels of GH prompt excessive growth.

gingiva – gum.

glabella – slight depression of frontal bone, located at the midline between the eyebrows.

glans penis – bulbous end of the penis that contains many nerve endings.

glenohumeral joint – shoulder joint; formed by the articulation between the glenoid cavity of the scapula and the head of the humerus.

glenohumeral ligament – one of the three intrinsic ligaments of the shoulder joint that strengthen the anterior articular capsule.

glenoid cavity – (also, glenoid fossa) shallow depression located on the lateral scapula, between the superior and lateral borders.

glenoid labrum – lip of fibrocartilage located around the outside margin of the glenoid cavity of the scapula.

glial cell – one of the various types of neural tissue cells responsible for maintenance of the tissue, and for supporting neurons.

globin – haem-containing globular protein that is a constituent of haemoglobin.

globulins – heterogeneous group of plasma proteins that includes transport proteins, clotting factors, immune proteins, and others.

globus pallidus – nuclei deep in the cerebrum that are part of the basal nuclei and can be divided into the internal and external segments.

glomerular filtration rate (GFR) – rate of renal filtration.

glomerulus – tuft of capillaries surrounded by Bowman’s capsule; filters the blood based on size.

glossopharyngeal nerve – ninth cranial nerve; responsible for contraction of muscles in the tongue and throat and for part of the sense of taste, as well as causing saliva production.

glottis – opening between the vocal folds through which air passes when producing speech.

glucagon – pancreatic hormone that stimulates the catabolism of glycogen to glucose, thereby increasing blood glucose levels.

glucocorticoids – hormones produced by the zona fasciculata of the adrenal cortex that influence glucose metabolism.

gluteal tuberosity – roughened area on the posterior side of the proximal femur, extending inferiorly from the base of the greater trochanter.

glycocalyx – coating of sugar molecules that surrounds the cell membrane.

glycogen – storage carbohydrate in animals.

glycolysis – anaerobic breakdown of glucose to ATP.

glycosidic bond – bond formed by a dehydration reaction between two monosaccharides with eliminating a water molecule.

glycoprotein – protein that has one or more carbohydrates attached.

glycosuria – presence of glucose in the urine; caused by high blood glucose levels that exceed the ability of the kidneys to reabsorb the glucose; usually the result of untreated or poorly controlled diabetes mellitus.

goblet cell – unicellular gland found in columnar epithelium that secretes mucous.

goitre – enlargement of the thyroid gland either as a result of iodine deficiency or hyperthyroidism.

Golgi apparatus – cellular organelle formed by a series of flattened, membrane-bound sacs that functions in protein modification, tagging, packaging, and transport.

gomphosis – type of fibrous joint in which the root of a tooth is anchored into its bony jaw socket by strong periodontal ligaments.

gonadal artery – branch of the abdominal aorta; supplies blood to the gonads or reproductive organs; also described as ovarian arteries or testicular arteries, depending upon the sex of the individual.

gonadal vein – generic term for a vein draining a reproductive organ; may be either an ovarian vein or a testicular vein, depending on the sex of the individual.

gonadotropins – hormones that regulate the function of the gonads.

gonadotropin-releasing hormone (GnRH) – hormone released by the hypothalamus that regulates the production of follicle-stimulating hormone and luteinizing hormone from the pituitary gland.

gonads – reproductive organs (testes in men and ovaries in women) that produce gametes and reproductive hormones.

G protein – guanosine triphosphate (GTP) hydrolase that physically moves from the receptor protein to the effector protein to activate the latter.

graded muscle response – modification of contraction strength.

graded potential – change in the membrane potential that varies in size, depending on the size of the stimulus that elicits it.

graft-versus-host disease – in bone marrow transplants; occurs when the transplanted cells mount an immune response against the recipient.

granular leukocytes – leukocytes with abundant granules in their cytoplasm; specifically, neutrophils, eosinophils, and basophils.

granulosa cells – supportive cells in the ovarian follicle that produce oestrogen.

granzyme – apoptosis-inducing substance contained in granules of NK cells and cytotoxic T cells.

great cardiac vein – vessel that follows the interventricular sulcus on the anterior surface of the heart and flows along the coronary sulcus into the coronary sinus on the posterior surface; parallels the anterior interventricular artery and drains the areas supplied by this vessel.

great cerebral vein – receives most of the smaller vessels from the inferior cerebral veins and leads to the straight sinus.

greater pelvis – (also, greater pelvic cavity or false pelvis) broad space above the pelvic brim defined laterally by the fan-like portion of the upper ilium.

great saphenous vein – prominent surface vessel located on the medial surface of the leg and thigh; drains the superficial portions of these areas and leads to the femoral vein.

greater sciatic foramen – pelvic opening formed by the greater sciatic notch of the hip bone, the sacrum, and the sacrospinous ligament.

greater sciatic notch – large, U-shaped indentation located on the posterior margin of the ilium, superior to the ischial spine.

greater trochanter – large, bony expansion of the femur that projects superiorly from the base of the femoral neck.

greater tubercle – enlarged prominence located on the lateral side of the proximal humerus.

greater wings of sphenoid bone – lateral projections of the sphenoid bone that form the anterior wall of the middle cranial fossa and an area of the lateral skull.

grey matter – regions of the nervous system containing cell bodies of neurons with few or no myelinated axons; typically may be more pink or tan in colour, but called grey in contrast to white matter.

gross anatomy – study of the larger structures of the body, typically with the unaided eye; also referred to macroscopic anatomy.

ground substance – fluid or semi-fluid portion of the matrix.

growth hormone (GH) – anterior pituitary hormone that promotes tissue building and influences nutrient metabolism (also called somatotropin).

gustation – sense of taste.

gustatory receptor cells – sensory cells in the taste bud that transduce the chemical stimuli of gustation.

gyrus – ridge formed by convolutions on the surface of the cerebrum or cerebellum.

G0 phase – phase of the cell cycle, usually entered from the G1 phase; characterised by long or permanent periods where the cell does not move forward into the DNA synthesis phase.

G1 phase – first phase of the cell cycle, after a new cell is born.

G2 phase – third phase of the cell cycle, after the DNA synthesis phase.

H

haem – red, iron-containing pigment to which oxygen binds in haemoglobin.

haemangioblasts – embryonic stem cells that appear in the mesoderm and give rise to both angioblasts and pluripotent stem cells.

haematocrit – (also, packed cell volume) volume percentage of erythrocytes in a sample of centrifuged blood.

haematopoiesis – production of blood cells, which occurs in the red marrow of the bones.

haemocytoblast – hemopoietic stem cell that gives rise to the formed elements of blood.

haemoglobin – oxygen-carrying globular protein in erythrocytes.

haemolysis – destruction (lysis) of erythrocytes and the release of their haemoglobin into circulation.

haemolytic disease of the foetus and newborn (HDFN) – (also, erythroblastosis fetalis) disorder causing agglutination and haemolysis in an Rh+ foetus or newborn of an Rh− mother.

haemopoiesis – production of the formed elements of blood.

haemopoietic growth factors – chemical signals including erythropoietin, thrombopoietin, colony-stimulating factors, and interleukins that regulate the differentiation and proliferation of particular blood progenitor cells.

haemopoietic stem cell – type of pluripotent stem cell that gives rise to the formed elements of blood (haemocytoblast).

haemosiderin – protein-containing storage form of iron found in the bone marrow, liver, and spleen.

haemophilia – genetic disorder characterised by inadequate synthesis of clotting factors.

haemorrhage – excessive bleeding.

haemostasis – physiological process by which bleeding ceases.

hair – keratinous filament growing out of the epidermis.

hair bulb – structure at the base of the hair root that surrounds the dermal papilla.

hair cells – mechanoreceptor cells found in the inner ear that transduce stimuli for the senses of hearing and balance.

hair follicle – cavity or sac from which hair originates.

hair matrix – layer of basal cells from which a strand of hair grows.

hair papilla – mass of connective tissue, blood capillaries, and nerve endings at the base of the hair follicle.

hair root – part of hair that is below the epidermis anchored to the follicle.

hair shaft – part of hair that is above the epidermis but is not anchored to the follicle.

Haldane effect – relationship between the partial pressure of oxygen and the affinity of haemoglobin for carbon dioxide.

hallux – big toe; digit 1 of the foot.

hamate – from the lateral side, the fourth of the four distal carpal bones; articulates with the lunate and triquetrum proximally, the fourth and fifth metacarpals distally, and the capitate laterally.

hand – region of the upper limb distal to the wrist joint.

hard palate – bony structure that forms the roof of the mouth and floor of the nasal cavity, formed by the palatine process of the maxillary bones and the horizontal plate of the palatine bones.

haustrum – small pouch in the colon created by tonic contractions of teniae coli.

haustral contraction – slow segmentation in the large intestine.

head of the femur – rounded, proximal end of the femur that articulates with the acetabulum of the hip bone to form the hip joint.

head of the fibula – small, knob-like, proximal end of the fibula; articulates with the inferior aspect of the lateral condyle of the tibia.

head of the humerus – smooth, rounded region on the medial side of the proximal humerus; articulates with the glenoid fossa of the scapula to form the glenohumeral (shoulder) joint.

head of the metatarsal bone – expanded, distal end of each metatarsal bone.

head of the radius – disc-shaped structure that forms the proximal end of the radius; articulates with the capitulum of the humerus as part of the elbow joint, and with the radial notch of the ulna as part of the proximal radioulnar joint.

head of the rib – posterior end of a rib that articulates with the bodies of thoracic vertebrae.

head of the ulna – small, rounded distal end of the ulna; articulates with the ulnar notch of the distal radius, forming the distal radioulnar joint.

heart block – interruption in the normal conduction pathway.

heart bulge – prominent feature on the anterior surface of the heart, reflecting early cardiac development.

heart rate (HR) – number of times the heart contracts (beats) per minute.

heart sounds – sounds heard via auscultation with a stethoscope of the closing of the atrioventricular valves (“lub”) and semilunar valves (“dub”).

heavy chain – larger protein chain of an antibody.

helicase – enzyme that functions to separate the two DNA strands of a double helix during DNA replication.

helper T cells (Th) – T cells that secrete cytokines to enhance other immune responses, involved in activation of both B and T cell lymphocytes.

hemiazygos vein – smaller vein complementary to the azygos vein; drains the oesophageal veins from the oesophagus and the left intercostal veins, and leads to the brachiocephalic vein via the superior intercostal vein.

Henry’s law – statement of the principle that the concentration of gas in a liquid is directly proportional to the solubility and partial pressure of that gas.

heparin – short-acting anticoagulant stored in mast cells and released when tissues are injured, opposes prothrombin.

hepatic artery – artery that supplies oxygenated blood to the liver.

hepatic artery proper – branch of the common hepatic artery; supplies systemic blood to the liver.

hepatic lobule – hexagonal-shaped structure composed of hepatocytes that radiate outward from a central vein.

hepatic portal system – specialised circulatory pathway that carries blood from digestive organs to the liver for processing before being sent to the systemic circulation.

hepatic portal vein – vein that supplies deoxygenated nutrient-rich blood to the liver.

hepatic sinusoid – blood capillaries between rows of hepatocytes that receive blood from the hepatic portal vein and the branches of the hepatic artery.

hepatic vein – drains systemic blood from the liver and flows into the inferior vena cava.

hepatocytes – major functional cells of the liver.

hepatopancreatic ampulla – (also, ampulla of Vater) bulb-like point in the wall of the duodenum where the bile duct and main pancreatic duct unite.

hepatopancreatic sphincter – (also, sphincter of Oddi) sphincter regulating the flow of bile and pancreatic secretion into the duodenum.

high endothelial venules – vessels containing unique endothelial cells specialised to allow migration of lymphocytes from the blood to the lymph node.

hilum – concave structure on the mediastinal surface of the lungs where blood vessels, lymphatic vessels, nerves, and a bronchus enter the lung.

hindbrain – posterior region of the adult brain that develops from the rhombencephalon and includes the pons, medulla oblongata, and cerebellum.

hinge joint – synovial joint at which the convex surface of one bone articulates with the concave surface of a second bone; includes the elbow, knee, ankle, and interphalangeal joints; functionally classified as a uniaxial joint.

hip bone – coxal bone; single bone that forms the pelvic girdle; consists of three areas, the ilium, ischium, and pubis.

hip joint – joint located at the proximal end of the lower limb; formed by the articulation between the acetabulum of the hip bone and the head of the femur.

hippocampus – grey matter deep in the temporal lobe that is very important for long-term memory formation.

histamine – chemical compound released by mast cells in response to injury that causes vasodilation and endothelium permeability.

histology – microscopic study of tissue architecture, organisation, and function.

histone – family of proteins that associate with DNA in the nucleus to form chromatin.

hole – opening or depression in a bone.

holocrine secretion – release of a substance caused by the rupture of a gland cell, which becomes part of the secretion.

homeostasis – steady state of body systems that living organisms maintain.

homologous – describes two copies of the same chromosome (not identical), one inherited from each parent.

hook of the hamate bone – bony extension located on the anterior side of the hamate carpal bone.

horizontal plate – medial extension from the palatine bone that forms the posterior quarter of the hard palate.

hormone – secretion of an endocrine organ that travels via the bloodstream or lymphatics to induce a response in target cells or tissues in another part of the body.

hormone receptor – protein within a cell or on the cell membrane that binds a hormone, initiating the target cell response.

human chorionic gonadotropin (hCG) – hormone that directs the corpus luteum to survive, enlarge, and continue producing progesterone and oestrogen to suppress menses and secure an environment suitable for the developing embryo.

humerus – single bone of the upper arm.

humeroradial joint – articulation between the capitulum of the humerus and head of the radius.

humeroulnar joint – articulation between the trochlea of humerus and the trochlear notch of the ulna; uniaxial hinge joint that allows for flexion/extension of the forearm.

hyaline cartilage – most common type of cartilage, smooth and made of short collagen fibres embedded in a chondroitin sulphate ground substance.

hydrochloric acid (HCl) – digestive acid secreted by parietal cells in the stomach.

hydrolysis – reaction that causes breakdown of larger molecules into smaller molecules by utilising water.

hydrophilic – describes a substance or structure attracted to water.

hydrophobic – describes a substance or structure repelled by water.

hydrostatic pressure – pressure exerted by a fluid against a wall, caused by its own weight or pumping force.

hymen – membrane that covers part of the opening of the vagina.

hyoid bone – small, U-shaped bone located in upper neck that does not contact any other bone.

hypercalcaemia – condition characterised by abnormally elevated levels of calcium.

hypercapnia – abnormally elevated blood levels of CO2.

hyperchloraemia – higher-than-normal blood chloride levels.

hyperextension – excessive extension of joint, beyond the normal range of movement.

hyperflexion – excessive flexion of joint, beyond the normal range of movement.

hyperglycaemia – abnormally high blood glucose levels.

hyperkalaemia – higher-than-normal blood potassium levels.

hypernatraemia – abnormal increase in blood sodium levels.

hyperparathyroidism – disorder caused by overproduction of PTH that results in abnormally elevated blood calcium.

hyperphosphataemia – abnormally increased blood phosphate levels.

hyperplasia – process in which one cell splits to produce new cells.

hyperpnoea – increased rate and depth of ventilation due to an increase in oxygen demand that does not significantly alter blood oxygen or carbon dioxide levels.

hypertension – chronic and persistent blood pressure measurements of 140/90 mm Hg or above.

hyperthyroidism – clinically abnormal, elevated level of thyroid hormone in the blood; characterised by an increased metabolic rate, excess body heat, sweating, diarrhoea, weight loss, and increased heart rate.

hypertonia – abnormally high muscle tone.

hypertonic – describes a solution concentration that is higher than a reference concentration.

hypertrophic cardiomyopathy – pathological enlargement of the heart, generally for no known reason.

hypertrophy – addition of structural proteins to muscle fibres.

hyperventilation – increased ventilation rate that leads to abnormally low blood carbon dioxide levels and high (alkaline) blood pH.

hypervolaemia – abnormally high levels of fluid and blood within the body.

hypoblast – lower layer of cells of the embryonic disc that extend into the blastocoel to form the yolk sac.

hypocalcaemia – condition characterised by abnormally low levels of calcium.

hypocapnia – abnormally low blood levels of CO2.

hypochloraemia – lower-than-normal blood chloride levels.

hypodermis – connective tissue connecting the integument to the underlying bone and muscle.

hypoglossal canal – paired openings that pass anteriorly from the anterior-lateral margins of the foramen magnum deep to the occipital condyles.

hypoglossal nerve – twelfth cranial nerve; responsible for contraction of muscles of the tongue.

hypokalaemia – abnormally decreased blood levels of potassium.

hyponatraemia – lower-than-normal levels of sodium in the blood.

hyponychium – thickened layer of stratum corneum that lies below the free edge of the nail.

hypoparathyroidism – disorder caused by underproduction of PTH that results in abnormally low blood calcium.

hypophosphataemia – abnormally low blood phosphate levels.

hypophyseal (pituitary) fossa – shallow depression on top of the sella turcica that houses the pituitary (hypophyseal) gland.

hypophyseal portal system – network of blood vessels that enables hypothalamic hormones to travel into the anterior lobe of the pituitary without entering the systemic circulation.

hypothalamus – major region of the diencephalon that is responsible for coordinating autonomic and endocrine control of homeostasis.

hypothyroidism – clinically abnormal, low level of thyroid hormone in the blood; characterised by low metabolic rate, weight gain, cold extremities, constipation, and reduced mental activity.

hypotonia – abnormally low muscle tone caused by the absence of low-level contractions.

hypotonic – describes a solution concentration that is lower than a reference concentration.

hypovolaemia – abnormally low levels of fluid and blood within the body.

hypovolaemic shock – type of circulatory shock caused by excessive loss of blood volume due to haemorrhage or possibly dehydration.

hypoxaemia – below-normal level of oxygen saturation of blood (typically <95 percent).

hypoxia – lack of oxygen supply to the tissues.

I

IgA – antibody whose dimer is secreted by exocrine glands, is especially effective against digestive and respiratory pathogens, and can pass immunity to an infant through breastfeeding.

IgD – class of antibody whose only known function is as a receptor on naive B cells; important in B cell activation.

IgE – antibody that binds to mast cells and causes antigen-specific degranulation during an allergic response.

IgG – main blood antibody of late primary and early secondary responses; passed from mother to unborn child via placenta.

IgM – antibody whose monomer is a surface receptor of naive B cells; the pentamer is the first antibody made blood plasma during primary responses.

iliac crest – curved, superior margin of the ilium.

iliac fossa – shallow depression found on the anterior and medial surfaces of the upper ilium.

ileocaecal sphincter – sphincter located where the small intestine joins with the large intestine.

ileum – end of the small intestine between the jejunum and the large intestine.

iliofemoral ligament – intrinsic ligament spanning from the ilium of the hip bone to the femur, on the superior-anterior aspect of the hip joint.

ilium – superior portion of the hip bone.

immediate hypersensitivity – (type I) IgE-mediated mast cell degranulation caused by crosslinking of surface IgE by antigen.

immune system – series of barriers, cells, and soluble mediators that combine to response to infections of the body with pathogenic organisms.

immunoglobulins – (also, antibodies or gamma globulins) antigen-specific proteins produced by specialised B lymphocytes that protect the body by binding to foreign objects such as bacteria and viruses.

immunological memory – ability of the adaptive immune response to mount a stronger and faster immune response upon re-exposure to a pathogen.

hypoblast – lower layer of cells of the embryonic disc that extend into the blastocoel to form the yolk sac.

inactivation gate – part of a voltage-gated Na⁺ channel that closes when the membrane potential reaches +30 mV.

incisor – midline, chisel-shaped tooth used for cutting into food.

incontinence – loss of ability to control micturition

incus – (also, anvil) ossicle of the middle ear that connects the malleus to the stapes.

indirect pathway – connections within the basal nuclei from the striatum through the globus pallidus external segment and subthalamic nucleus to the globus pallidus internal segment/substantia nigra pars compacta that result in inhibition of the thalamus to decrease cortical control of movement.

inferior – describes a position below or lower than another part of the body proper; near or toward the tail (in humans, the coccyx, or lowest part of the spinal column); also referred to as caudal.

inferior angle of the scapula – inferior corner of the scapula located where the medial and lateral borders meet.

inferior articular process – bony process that extends downward from the vertebral arch of a vertebra that articulates with the superior articular process of the next lower vertebra.

inferior colliculus – half of the midbrain tectum that is part of the brain stem auditory pathway.

inferior mesenteric artery – branch of the abdominal aorta; supplies blood to the distal segment of the large intestine and rectum.

inferior nasal concha – one of the paired bones that project from the lateral walls of the nasal cavity to form the largest and most inferior of the nasal conchae.

inferior oblique – extraocular muscle responsible for lateral rotation of the eye.

inferior olive – nucleus in the medulla that is involved in processing information related to motor control.

inferior phrenic artery – branch of the abdominal aorta; supplies blood to the inferior surface of the diaphragm.

inferior pubic ramus – narrow segment of bone that passes inferiorly and laterally from the pubic body; joins with the ischial ramus to form the ischiopubic ramus.

inferior rectus – extraocular muscle responsible for looking down.

inferior rotation – movement of the scapula during upper limb adduction in which the glenoid cavity of the scapula moves in a downward direction as the medial end of the scapular spine moves in an upward direction.

inferior vena cava – large systemic vein that returns blood to the heart from the inferior portion of the body.

inflammation – response of tissue to injury.

infraglenoid tubercle – small bump or roughened area located on the lateral border of the scapula, near the inferior margin of the glenoid cavity.

infraorbital foramen – opening located on anterior skull, below the orbit.

infraspinous fossa – broad depression located on the posterior scapula, inferior to the spine.

infratemporal fossa – space on lateral side of skull, below the level of the zygomatic arch and deep (medial) to the ramus of the mandible.

infundibulum – stalk containing vasculature and neural tissue that connects the pituitary gland to the hypothalamus (also called the pituitary stalk).

infundibulum – (of the uterine tube) wide, distal portion of the uterine tube terminating in fimbriae.

ingestion – taking food into the GI tract through the mouth.

inguinal canal – opening in abdominal wall that connects the testes to the abdominal cavity.

inhibin – hormone secreted by the male and female gonads that inhibits FSH production by the anterior pituitary.

inhibitory postsynaptic potential (IPSP) – graded potential in the postsynaptic membrane that is the result of hyperpolarisation and makes an action potential less likely to occur.

initial segment – first part of the axon as it emerges from the axon hillock, where the electrical signals known as action potentials are generated.

innate immune response – rapid but relatively nonspecific immune response.

inner cell mass – cluster of cells within the blastocyst that is fated to become the embryo.

inner ear – structure within the temporal bone that contains the sensory apparati of hearing and balance.

inner segment – in the eye, the section of a photoreceptor that contains the nucleus and other major organelles for normal cellular functions.

inner synaptic layer – layer in the retina where bipolar cells connect to RGCs.

inositol triphosphate (IP3) – molecule that initiates the release of calcium ions from intracellular stores.

inspiration – (also, inhalation) process that causes air to enter the lungs.

inspiratory capacity (IC) – sum of the TV and IRV, which is the amount of air that can maximally be inhaled past a tidal expiration.

inspiratory reserve volume (IRV) – amount of air that enters the lungs due to deep inhalation past the tidal volume.

insulin – pancreatic hormone that enhances the cellular uptake and utilisation of glucose, thereby decreasing blood glucose levels.

insulin-like growth factors (IGF) – protein that enhances cellular proliferation, inhibits apoptosis, and stimulates the cellular uptake of amino acids for protein synthesis.

integral protein – membrane-associated protein that spans the entire width of the lipid bilayer.

integration – nervous system function that combines sensory perceptions and higher cognitive functions (memories, learning, emotion, etc.) to produce a response.

integumentary system – skin and its accessory structures.

interatrial band – (also, Bachmann’s bundle) group of specialised conducting cells that transmit the impulse directly from the SA node in the right atrium to the left atrium.

interatrial septum – cardiac septum located between the two atria; contains the fossa ovalis after birth.

interaural intensity difference – cue used to aid sound localisation in the horizontal plane that compares the relative loudness of sounds at the two ears, because the ear closer to the sound source will hear a slightly more intense sound.

interaural time difference – cue used to help with sound localisation in the horizontal plane that compares the relative time of arrival of sounds at the two ears, because the ear closer to the sound source will receive the stimulus microseconds before the other ear.

intercalated cell – specialised cell of the collecting ducts that secrete or absorb acid or bicarbonate; important in acid–base balance.

intercalated disc – physical junction between adjacent cardiac muscle cells; consisting of desmosomes, specialised linking proteoglycans, and gap junctions that allow passage of ions between the two cells.

intercondylar eminence – irregular elevation on the superior end of the tibia, between the articulating surfaces of the medial and lateral condyles.

intercondylar fossa – deep depression on the posterior side of the distal femur that separates the medial and lateral condyles.

intercostal artery – branch of the thoracic aorta; supplies blood to the muscles of the thoracic cavity and vertebral column.

intercostal nerve – systemic nerve in the thoracic cavity that is found between two ribs.

intercostal vein – drains the muscles of the thoracic wall and leads to the azygos vein.

interferons – early induced proteins made in virally infected cells that cause nearby cells to make antiviral proteins.

interleukins – signalling molecules that may function in haemopoiesis, inflammation, and specific immune responses.

intermediate cuneiform – middle of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, medially with the medial cuneiform bone, laterally with the lateral cuneiform bone, and anteriorly with the second metatarsal bone.

intermediate filament – type of cytoskeletal filament made of keratin, characterised by an intermediate thickness, and playing a role in resisting cellular tension.

internal acoustic meatus – opening into petrous ridge, located on the lateral wall of the posterior cranial fossa.

internal anal sphincter – involuntary smooth muscle sphincter in the anal canal.

internal callus – fibrocartilaginous matrix, in the endosteal region, between the two ends of a broken bone.

internal capsule – segment of the descending motor pathway that passes between the caudate nucleus and the putamen.

internal carotid artery – arises from the common carotid artery and begins with the carotid sinus; goes through the carotid canal of the temporal bone to the base of the brain; combines with branches of the vertebral artery forming the arterial circle; supplies blood to the brain.

internal elastic membrane – membrane composed of elastic fibres that separates the tunica intima from the tunica media; seen in larger arteries.

internal iliac artery – branch from the common iliac arteries; supplies blood to the urinary bladder, walls of the pelvis, external genitalia, and the medial portion of the femoral region; in females, also provide blood to the uterus and vagina.

internal iliac vein – drains the pelvic organs and integument; formed from several smaller veins in the region; leads to the common iliac vein.

internal jugular vein – one of a pair of major veins located in the neck region that passes through the jugular foramen and canal, flows parallel to the common carotid artery that is more or less its counterpart; primarily drains blood from the brain, receives the superficial facial vein, and empties into the subclavian vein.

internal respiration – gas exchange that occurs at the level of body tissues.

internal root sheath – innermost layer of keratinocytes in the hair follicle that surround the hair root up to the hair shaft.

internal thoracic artery – (also, mammary artery) arises from the subclavian artery; supplies blood to the thymus, pericardium of the heart, and the anterior chest wall.

internal thoracic vein – (also, internal mammary vein) drains the anterior surface of the chest wall and leads to the brachiocephalic vein.

internal urinary sphincter – smooth muscle at the juncture of the bladder and urethra; relaxes as the bladder fills to allow urine into the urethra

internodal pathways – specialised conductile cells within the atria that transmit the impulse from the SA node throughout the myocardial cells of the atrium and to the AV node.

interoceptor – sensory receptor that is positioned to interpret stimuli from internal organs, such as stretch receptors in the wall of blood vessels.

interosseous border of the fibula – small ridge running down the medial side of the fibular shaft; for attachment of the interosseous membrane between the fibula and tibia.

interosseous border of the radius – narrow ridge located on the medial side of the radial shaft; for attachment of the interosseous membrane between the ulna and radius bones.

interosseous border of the tibia – small ridge running down the lateral side of the tibial shaft; for attachment of the interosseous membrane between the tibia and fibula.

interosseous border of the ulna – narrow ridge located on the lateral side of the ulnar shaft; for attachment of the interosseous membrane between the ulna and radius.

interosseous membrane – wide sheet of fibrous connective tissue that fills the gap between two parallel bones, forming a syndesmosis; found between the radius and ulna of the forearm and between the tibia and fibula of the leg.

interosseous membrane of the forearm – sheet of dense connective tissue that unites the radius and ulna bones.

interosseous membrane of the leg – sheet of dense connective tissue that unites the shafts of the tibia and fibula bones.

interphalangeal joint – articulation between adjacent phalanx bones of the hand or foot digits.

interphase – entire life cycle of a cell, excluding mitosis.

interstitial fluid (IF) – fluid in the small spaces between cells not contained within blood vessels.

interstitial fluid colloidal osmotic pressure (IFCOP) – pressure exerted by the colloids within the interstitial fluid.

interstitial fluid hydrostatic pressure (IFHP) – force exerted by the fluid in the tissue spaces.

intertrochanteric crest – short, prominent ridge running between the greater and lesser trochanters on the posterior side of the proximal femur.

intertrochanteric line – small ridge running between the greater and lesser trochanters on the anterior side of the proximal femur.

intertubercular groove (sulcus) – bicipital groove; narrow groove located between the greater and lesser tubercles of the humerus.

interventricular foramina – openings between the lateral ventricles and third ventricle allowing for the passage of CSF.

interventricular septum – cardiac septum located between the two ventricles.

intervertebral disc – structure located between the bodies of adjacent vertebrae that strongly joins the vertebrae; provides padding, weight bearing ability, and enables vertebral column movements.

intervertebral foramen – opening located between adjacent vertebrae for exit of a spinal nerve.

intestinal gland – (also, crypt of Lieberkühn) gland in the small intestinal mucosa that secretes intestinal secretion.

intestinal phase – phase of gastric secretion that begins when chyme enters the intestine.

intestinal secretion – mixture of water and mucus that helps absorb nutrients from chyme.

intra-alveolar pressure – (intrapulmonary pressure) pressure of the air within the alveoli.

intracapsular ligament – ligament that is located within the articular capsule of a synovial joint.

intracellular fluid (ICF) – fluid in the cytosol of cells.

intramembranous ossification – process by which bone forms directly from mesenchymal tissue.

intrapleural pressure – pressure of the air within the pleural cavity.

intrinsic ligament – ligament that is fused to or incorporated into the wall of the articular capsule of a synovial joint.

intrinsic factor – glycoprotein required for vitamin B12 absorption in the small intestine.

intrinsic pathway – initial coagulation pathway that begins with vascular damage or contact with foreign substances, and results in the activation of the common pathway.

intron – non-coding regions of a pre-mRNA transcript that may be removed during splicing.

inulin – plant polysaccharide injected to determine GFR; is neither secreted nor absorbed by the kidney, so its appearance in the urine is directly proportional to its filtration rate.

inversion – foot movement involving the intertarsal joints of the foot in which the bottom of the foot is turned toward the midline.

ionotropic receptor – neurotransmitter receptor that acts as an ion channel gate, and opens by the binding of the neurotransmitter.

ipsilateral – word meaning on the same side, as in axons that do not cross the midline in a fibre tract.

iris – coloured portion of the anterior eye that surrounds the pupil.

irregular bone – bone of complex shape; protects internal organs from compressive forces.

ischaemia – insufficient blood flow to the tissues.

ischial ramus – bony extension projecting anteriorly and superiorly from the ischial tuberosity; joins with the inferior pubic ramus to form the ischiopubic ramus.

ischial spine – pointed, bony projection from the posterior margin of the ischium that separates the greater sciatic notch and lesser sciatic notch.

ischial tuberosity – large, roughened protuberance that forms the posteroinferior portion of the hip bone; weight-bearing region of the pelvis when sitting.

ischiofemoral ligament – intrinsic ligament spanning from the ischium of the hip bone to the femur, on the posterior aspect of the hip joint.

ischiopubic ramus – narrow extension of bone that connects the ischial tuberosity to the pubic body; formed by the junction of the ischial ramus and inferior pubic ramus.

ischium – posteroinferior portion of the hip bone.

isometric contraction – muscle contraction that occurs with no change in muscle length.

isotonic – describes a solution concentration that is the same as a reference concentration.

isotonic contraction – muscle contraction that involves changes in muscle length.

isovolumic contraction – (also, isovolumetric contraction) initial phase of ventricular contraction in which tension and pressure in the ventricle increase, but no blood is pumped or ejected from the heart.

isovolumic ventricular relaxation phase – initial phase of the ventricular diastole when pressure in the ventricles drops below pressure in the two major arteries, the pulmonary trunk, and the aorta, and blood attempts to flow back into the ventricles, producing the dicrotic notch of the ECG and closing the two semilunar valves.

isthmus – narrow, medial portion of the uterine tube that joins the uterus.

J

jejunum – middle part of the small intestine between the duodenum and the ileum.

joint – site at which two or more bones or bone and cartilage come together (articulate).

joint cavity – space enclosed by the articular capsule of a synovial joint that is filled with synovial fluid and contains the articulating surfaces of the adjacent bones.

joint interzone – site within a growing embryonic limb bud that will become a synovial joint.

jugular foramen – irregularly shaped opening located in the lateral floor of the posterior cranial cavity.

jugular (suprasternal) notch – shallow notch located on superior surface of sternal manubrium.

jugular veins – blood vessels that return “used” blood from the head and neck.

juxtaglomerular apparatus (JGA) – located at the juncture of the DCT and the afferent and efferent arterioles of the glomerulus; plays a role in the regulation of renal blood flow and GFR.

juxtaglomerular cell – modified smooth muscle cells of the afferent arteriole; secretes renin in response to a drop in blood pressure.

juxtamedullary nephrons – nephrons adjacent to the border of the cortex and medulla with loops of Henle that extend into the renal medulla.

K

keloid – type of scar that has layers raised above the skin surface.

keratin – type of structural protein that gives skin, hair, and nails its hard, water-resistant properties.

keratinocyte – cell that produces keratin and is the most predominant type of cell found in the epidermis.

keratohyalin – granulated protein found in the stratum granulosum.

kinaesthesia – general sensory perception of movement of the body.

kinetochore – region of a centromere where microtubules attach to a pair of sister chromatids.

knee joint – joint that separates the thigh and leg portions of the lower limb; formed by the articulations between the medial and lateral condyles of the femur, and the medial and lateral condyles of the tibia.

Korotkoff sounds – noises created by turbulent blood flow through the vessels.

kyphosis – (also, humpback or hunchback) excessive posterior curvature of the thoracic vertebral column region.

L

labia majora – hair-covered folds of skin located behind the mons pubis.

labia minora – thin, pigmented, hairless flaps of skin located medial and deep to the labia majora.

labium – lip.

labial frenulum – midline mucous membrane fold that attaches the inner surface of the lips to the gums.

lacrimal bone – paired bones that contribute to the anterior-medial wall of each orbit.

lacrimal duct – duct in the medial corner of the orbit that drains tears into the nasal cavity.

lacrimal fossa – shallow depression in the anterior-medial wall of the orbit, formed by the lacrimal bone that gives rise to the nasolacrimal canal.

lacrimal gland – gland lateral to the orbit that produces tears to wash across the surface of the eye.

lactase – brush border enzyme that breaks down lactose into glucose and galactose.

lacteal – lymphatic capillary in the villi.

lactic acid – product of anaerobic glycolysis.

lactiferous ducts – ducts that connect the mammary glands to the nipple and allow for the transport of milk.

lactiferous sinus – area of milk collection between alveoli and lactiferous duct.

lacunae – (singular = lacuna) small spaces in bone or cartilage tissue that cells occupy.

lambdoid suture – inverted V-shaped joint that unites the occipital bone to the right and left parietal bones on the posterior skull.

lamina – portion of the vertebral arch on each vertebra that extends between the transverse and spinous process.

lamina propria – areolar connective tissue underlying a mucous membrane.

Langerhans cell – specialised dendritic cell found in the stratum spinosum that functions as a macrophage.

lanugo – silk-like hairs that coat the foetus; shed later in foetal development.

large intestine – terminal portion of the gastrointestinal tract.

laryngeal prominence – region where the two lamina of the thyroid cartilage join, forming a protrusion known as “Adam’s apple”.

laryngopharynx – portion of the pharynx bordered by the oropharynx superiorly and oesophagus and trachea inferiorly; serves as a route for both air and food.

laryngotracheal – bud forms from the lung bud, has a tracheal end and bulbous bronchial buds at the distal end.

larynx – cartilaginous structure that produces the voice, prevents food and beverages from entering the trachea, and regulates the volume of air that enters and leaves the lungs.

latch-bridges – subset of a cross-bridge in which actin and myosin remain locked together.

latent period – the time when a twitch does not produce contraction.

lateral – describes the side or direction toward the side of the body.

lateral apertures – pair of openings from the fourth ventricle to the subarachnoid space on either side and between the medulla and cerebellum.

lateral border of the scapula – diagonally oriented lateral margin of the scapula.

lateral circumflex artery – branch of the deep femoral artery; supplies blood to the deep muscles of the thigh and the ventral and lateral regions of the integument.

lateral column – white matter of the spinal cord between the posterior horn on one side and the axons from the anterior horn on the same side; composed of many different groups of axons, of both ascending and descending tracts, carrying motor commands to and from the brain.

lateral condyle of the femur – smooth, articulating surface that forms the distal and posterior sides of the lateral expansion of the distal femur.

lateral condyle of the tibia – lateral, expanded region of the proximal tibia that includes the smooth surface that articulates with the lateral condyle of the femur as part of the knee joint.

lateral corticospinal tract – division of the corticospinal pathway that travels through the lateral column of the spinal cord and controls appendicular musculature through the lateral motor neurons in the ventral (anterior) horn.

lateral cuneiform – most lateral of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, medially with the intermediate cuneiform bone, laterally with the cuboid bone, and anteriorly with the third metatarsal bone.

lateral epicondyle of the femur – roughened area of the femur located on the lateral side of the lateral condyle.

lateral epicondyle of the humerus – small projection located on the lateral side of the distal humerus.

lateral excursion – side-to-side movement of the mandible away from the midline, toward either the right or left side.

lateral flexion – bending of the neck or body toward the right or left side.

lateral geniculate nucleus – thalamic target of the RGCs that projects to the visual cortex.

lateral horn – region of the spinal cord grey matter in the thoracic, upper lumbar, and sacral regions that is the central component of the sympathetic division of the autonomic nervous system.

lateral malleolus – expanded distal end of the fibula.

lateral meniscus – C-shaped fibrocartilage articular disc located at the knee, between the lateral condyle of the femur and the lateral condyle of the tibia.

lateral plantar artery – arises from the bifurcation of the posterior tibial arteries; supplies blood to the lateral plantar surfaces of the foot.

lateral pterygoid plate – paired, flattened bony projections of the sphenoid bone located on the inferior skull, lateral to the medial pterygoid plate.

lateral rectus – extraocular muscle responsible for abduction of the eye.

lateral (external) rotation – movement of the arm at the shoulder joint or the thigh at the hip joint that moves the anterior surface of the limb away from the midline of the body.

lateral sacral crest – paired irregular ridges running down the lateral sides of the posterior sacrum that was formed by the fusion of the transverse processes from the five sacral vertebrae.

lateral sulcus – surface landmark of the cerebral cortex that marks the boundary between the temporal lobe and the frontal and parietal lobes.

lateral supracondylar ridge – narrow, bony ridge located along the lateral side of the distal humerus, superior to the lateral epicondyle.

lateral tibiofemoral joint – portion of the knee consisting of the articulation between the lateral condyle of the tibia and the lateral condyle of the femur; allows for flexion/extension at the knee.

lateral ventricles – portions of the ventricular system that are in the region of the cerebrum.

leakage channel – ion channel that opens randomly and is not gated to a specific event, also known as a non-gated channel.

leaky tight junctions – tight junctions in which the sealing strands of proteins between the membranes of adjacent cells are fewer in number and incomplete; allows limited intercellular movement of solvent and solutes.

left atrioventricular valve – (also, mitral valve or bicuspid valve) valve located between the left atrium and ventricle; consists of two flaps of tissue.

left colic flexure – (also, splenic flexure) point where the transverse colon curves below the inferior end of the spleen.

left gastric artery – branch of the celiac trunk; supplies blood to the stomach.

leg – portion of the lower limb located between the knee and ankle joints.

lens – component of the eye that focuses light on the retina.

leptin – protein hormone secreted by adipose tissues in response to food consumption that promotes satiety.

lesser pelvis – (also, lesser pelvic cavity or true pelvis) narrow space located within the pelvis, defined superiorly by the pelvic brim (pelvic inlet) and inferiorly by the pelvic outlet.

lesser sciatic foramen – pelvic opening formed by the lesser sciatic notch of the hip bone, the sacrospinous ligament, and the sacrotuberous ligament.

lesser sciatic notch – shallow indentation along the posterior margin of the ischium, inferior to the ischial spine.

lesser trochanter – small, bony projection on the medial side of the proximal femur, at the base of the femoral neck.

lesser tubercle – small, bony prominence located on anterior side of the proximal humerus.

lesser wings of the sphenoid bone – lateral extensions of the sphenoid bone that form the bony lip separating the anterior and middle cranial fossae.

leukaemia – cancer involving leukocytes.

leukocyte – (also, white blood cell) colourless, nucleated blood cell, the chief function of which is to protect the body from disease.

leukocyte esterase – enzyme produced by leukocytes that can be detected in the urine and that serves as an indirect indicator of urinary tract infection.

leukocytosis – excessive leukocyte proliferation.

leukopenia – below-normal production of leukocytes.

levator palpebrae superioris – muscle that causes elevation of the upper eyelid, controlled by fibres in the oculomotor nerve.

Leydig cells – cells between the seminiferous tubules of the testes that produce testosterone, a type of interstitial cell.

ligament – strong band of dense connective tissue spanning between bones.

ligament of the head of the femur – ligament that spans the acetabulum of the hip bone and the fovea capitis of the femoral head.

ligamentum flavum – series of short ligaments that unite the lamina of adjacent vertebrae.

ligand – molecule that binds with specificity to a specific receptor molecule.

ligand-gated channels – another name for an ionotropic receptor for which a neurotransmitter is the ligand.

light chain – small protein chain of an antibody.

limb bud – small elevation that appears on the lateral side of the embryo during the fourth or fifth week of development, which gives rise to an upper or lower limb.

limbic cortex – collection of structures of the cerebral cortex that are involved in emotion, memory, and behaviour and are part of the larger limbic system.

limbic system – structures at the edge (limit) of the boundary between the forebrain and hindbrain that are most associated with emotional behaviour and memory formation.

linea aspera – longitudinally running bony ridge located in the middle third of the posterior femur.

lingual frenulum – mucous membrane fold that attaches the bottom of the tongue to the floor of the mouth.

lingual lipase – digestive enzyme from glands in the tongue that acts on triglycerides.

lingual tonsil – lymphoid tissue located at the base of the tongue.

lingula – small flap of bone located on the inner (medial) surface of mandibular ramus, next to the mandibular foramen.

lipid – macromolecule that is nonpolar and insoluble in water.

lipoprotein lipase – enzyme that breaks down triglycerides in chylomicrons into fatty acids and monoglycerides.

liver – largest gland in the body whose main digestive function is the production of bile.

long bone – cylinder-shaped bone that is longer than it is wide; functions as a lever.

longitudinal fissure – large separation along the midline between the two cerebral hemispheres.

loop of Henle – descending and ascending portions between the proximal and distal convoluted tubules; those of cortical nephrons do not extend into the medulla, whereas those of juxtamedullary nephrons do extend into the medulla.

loose connective tissue – (also, areolar tissue) type of connective tissue proper that shows little specialisation with cells dispersed in the matrix.

lordosis – (also, swayback) excessive anterior curvature of the lumbar vertebral column region.

lower motor neuron – second neuron in the motor command pathway that is directly connected to the skeletal muscle.

lower oesophageal sphincter – smooth muscle sphincter that regulates food movement from the oesophagus to the stomach.

lumbar arteries – branches of the abdominal aorta; supply blood to the lumbar region, the abdominal wall, and spinal cord.

lumbar curve – posteriorly concave curvature of the lumbar vertebral column region; a secondary curve of the vertebral column.

lumbar enlargement – region of the ventral (anterior) horn of the spinal cord that has a larger population of motor neurons for the greater number of muscles of the lower limb.

lumbar plexus – nerve plexus associated with the lumbar spinal nerves.

lumbar puncture – procedure used to withdraw CSF from the lower lumbar region of the vertebral column that avoids the risk of damaging CNS tissue because the spinal cord ends at the upper lumbar vertebrae.

lumbar veins – drain the lumbar portion of the abdominal wall and spinal cord; the superior lumbar veins drain into the azygos vein on the right or the hemiazygos vein on the left; blood from these vessels is returned to the superior vena cava rather than the inferior vena cava.

lumbar vertebrae – five vertebrae numbered as L1–L5 that are located in lumbar region (lower back) of the vertebral column.

lumen – interior of a tubular structure such as a blood vessel or a portion of the alimentary canal through which blood, chyme, or other substances travel.

lunate – from the lateral side, the second of the four proximal carpal bones; articulates with the radius proximally, the capitate and hamate distally, the scaphoid laterally, and the triquetrum medially.

lung – organ of the respiratory system that performs gas exchange.

lung bud – median dome that forms from the endoderm of the foregut.

lunula – basal part of the nail body that consists of a crescent-shaped layer of thick epithelium.

luteinising hormone (LH) – anterior pituitary hormone that triggers ovulation and the production of ovarian hormones in females, and the production of testosterone in males.

lymph – fluid contained within the lymphatic system.

lymphocytes – agranular leukocytes of the lymphoid stem cell line, many of which function in specific immunity.

lymphoid stem cells – type of haemopoietic stem cells that gives rise to lymphocytes, including various T cells, B cells, and NK cells, all of which function in immunity.

lymphoma – form of cancer in which masses of malignant T and/or B lymphocytes collect in lymph nodes, the spleen, the liver, and other tissues.

lymph node – one of the bean-shaped organs found associated with the lymphatic vessels.

lymphatic capillaries – smallest of the lymphatic vessels and the origin of lymph flow.

lymphatic system – network of lymphatic vessels, lymph nodes, and ducts that carries lymph from the tissues and back to the bloodstream.

lymphatic trunks – large lymphatics that collect lymph from smaller lymphatic vessels and empties into the blood via lymphatic ducts.

lymphocytes – white blood cells characterised by a large nucleus and small rim of cytoplasm.

lymphoid nodules – unencapsulated patches of lymphoid tissue found throughout the body.

lysozyme – digestive enzyme with bactericidal properties.

lysosome – membrane-bound cellular organelle originating from the Golgi apparatus and containing digestive enzymes.

M

macrophage – phagocytic cell of the myeloid lineage; a matured monocyte.

macrophage oxidative metabolism – metabolism turned on in macrophages by T cell signals that help destroy intracellular bacteria.

macula – enlargement at the base of a semicircular canal at which transduction of equilibrium stimuli takes place within the ampulla.

macula densa – cells found in the part of the DCT forming the JGA; sense Na+ concentration in the forming urine.

main pancreatic duct – (also, duct of Wirsung) duct through which pancreatic secretion drains from the pancreas.

major duodenal papilla – point at which the hepatopancreatic ampulla opens into the duodenum.

major histocompatibility complex (MHC) – gene cluster whose proteins present antigens to T cells.

malleus – (also, hammer) ossicle that is directly attached to the tympanic membrane.

maltase – brush border enzyme that breaks down maltose and maltotriose into two and three molecules of glucose, respectively.

mammary glands – glands inside the breast that secrete milk.

mandible – unpaired bone that forms the lower jaw bone; the only moveable bone of the skull.

mandibular foramen – opening located on the inner (medial) surface of the mandibular ramus.

mandibular fossa – oval depression located on the inferior surface of the skull.

mandibular notch – large U-shaped notch located between the condylar process and coronoid process of the mandible.

manubrium – expanded, superior portion of the sternum.

marginal arteries – branches of the right coronary artery that supply blood to the superficial portions of the right ventricle.

mass movement – long, slow, peristaltic wave in the large intestine.

mast cell – cell found in the skin and the lining of body cells that contains cytoplasmic granules with vasoactive mediators such as histamine.

mastication – chewing.

mastoid process – large bony prominence on the inferior, lateral skull, just behind the earlobe.

matrix – extracellular material which is produced by the cells embedded in it, containing ground substance and fibres.

maxillary bone – (also, maxilla) paired bones that form the upper jaw and anterior portion of the hard palate.

maxillary sinus – air-filled space located with each maxillary bone; largest of the paranasal sinuses.

maxillary vein – drains blood from the maxillary region and leads to the external jugular vein.

mean arterial pressure (MAP) – average driving force of blood to the tissues; approximated by taking diastolic pressure and adding 1/3 of pulse pressure.

meatus – one of three recesses (superior, middle, and inferior) in the nasal cavity attached to the conchae that increase the surface area of the nasal cavity.

mechanical digestion – chewing, mixing, and segmentation that prepares food for chemical digestion.

mechanically gated channel – ion channel that opens when a physical event directly affects the structure of the protein.

mechanoreceptor – receptor cell that transduces mechanical stimuli into an electrochemical signal.

meconium – foetal wastes consisting of ingested amniotic fluid, cellular debris, mucus, and bile.

medial – describes the middle or direction toward the middle of the body.

medial border of the scapula – elongated, medial margin of the scapula.

medial condyle of the femur – smooth, articulating surface that forms the distal and posterior sides of the medial expansion of the distal femur.

medial condyle of the tibia – medial, expanded region of the proximal tibia that includes the smooth surface that articulates with the medial condyle of the femur as part of the knee joint.

medial cuneiform – most medial of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, laterally with the intermediate cuneiform bone, and anteriorly with the first and second metatarsal bones.

medial epicondyle of the femur – roughened area of the distal femur located on the medial side of the medial condyle.

medial epicondyle of the humerus – enlarged projection located on the medial side of the distal humerus.

medial excursion – side-to-side movement that returns the mandible to the midline.

medial geniculate nucleus – thalamic target of the auditory brain stem that projects to the auditory cortex.

medial lemniscus – fibre tract of the dorsal column system that extends from the nuclei gracilis and cuneatus to the thalamus, and decussates.

medial malleolus – bony expansion located on the medial side of the distal tibia.

medial meniscus – C-shaped fibrocartilage articular disc located at the knee, between the medial condyle of the femur and medial condyle of the tibia.

medial plantar artery – arises from the bifurcation of the posterior tibial arteries; supplies blood to the medial plantar surfaces of the foot.

medial pterygoid plate – paired, flattened bony projections of the sphenoid bone located on the inferior skull medial to the lateral pterygoid plate; form the posterior portion of the nasal cavity lateral wall.

medial rectus – extraocular muscle responsible for adduction of the eye.

medial (internal) rotation – movement of the arm at the shoulder joint or the thigh at the hip joint that brings the anterior surface of the limb toward the midline of the body.

medial tibiofemoral joint – portion of the knee consisting of the articulation between the medial condyle of the tibia and the medial condyle of the femur; allows for flexion/extension at the knee.

median antebrachial vein – vein that parallels the ulnar vein but is more medial in location; intertwines with the palmar venous arches.

median aperture – singular opening from the fourth ventricle into the subarachnoid space at the midline between the medulla and cerebellum.

median cubital vein – superficial vessel located in the antecubital region that links the cephalic vein to the basilic vein in the form of a v; a frequent site for a blood draw.

median nerve – systemic nerve of the arm, located between the ulnar and radial nerves.

median sacral artery – continuation of the aorta into the sacrum.

median sacral crest – irregular ridge running down the midline of the posterior sacrum that was formed from the fusion of the spinous processes of the five sacral vertebrae.

mediastinal artery – branch of the thoracic aorta; supplies blood to the mediastinum.

medulla – in hair, the innermost layer of keratinocytes originating from the hair matrix.

medulla – inner region of kidney containing the renal pyramids.

medullary cavity – hollow region of the diaphysis; filled with yellow marrow.

megakaryocyte – bone marrow cell that produces platelets.

Meissner corpuscle – (also, tactile corpuscle) receptor in the skin that responds to light touch.

melanin – pigment that determines the colour of hair and skin.

melanocyte – cell found in the stratum basale of the epidermis that produces the pigment melanin.

melanoma – type of skin cancer that originates from the melanocytes of the skin.

melanosome – intercellular vesicle that transfers melanin from melanocytes into keratinocytes of the epidermis.

melatonin – amino acid–derived hormone that is secreted in response to low light and causes drowsiness.

membrane potential – distribution of charge across the cell membrane, based on the charges of ions.

memory cell – type of B or T lymphocyte that forms after exposure to a pathogen.

memory T cells – long-lived immune cell reserved for future exposure to a pathogen.

menarche – first menstruation in a pubertal female.

meninges – protective outer coverings of the CNS composed of connective tissue.

meniscus – articular disc.

menses – shedding of the inner portion of the endometrium out though the vagina; also referred to as menstruation.

menses phase – phase of the menstrual cycle in which the endometrial lining is shed.

menstrual cycle – approximately 28-day cycle of changes in the uterus consisting of a menses phase, a proliferative phase, and a secretory phase.

mental foramen – opening located on the anterior-lateral side of the mandibular body.

mental protuberance – inferior margin of anterior mandible that forms the chin.

Merkel cell – receptor cell in the stratum basale of the epidermis that responds to the sense of touch.

merocrine secretion – release of a substance from a gland via exocytosis.

mesangial – contractile cells found in the glomerulus; can contract or relax to regulate filtration rate.

mesencephalic nucleus – component of the trigeminal nuclei that is found in the midbrain.

mesencephalon – primary vesicle of the embryonic brain that does not significantly change through the rest of embryonic development and becomes the midbrain.

mesenchymal cell – adult stem cell from which most connective tissue cells are derived.

mesenchyme – embryonic tissue from which connective tissue cells derive.

mesoappendix – mesentery of the appendix.

mesoderm – middle embryonic germ layer from which connective tissue, muscle tissue, and some epithelial tissue derive.

mesothelium – simple squamous epithelial tissue which covers the major body cavities and is the epithelial portion of serous membranes.

messenger RNA (mRNA) – nucleotide molecule that serves as an intermediate in the genetic code between DNA and protein.

metabolic acidosis – condition wherein a deficiency of bicarbonate causes the blood to be overly acidic.

metabolic alkalosis – condition wherein an excess of bicarbonate causes the blood to be overly alkaline.

metabotropic receptor – neurotransmitter receptor that involves a complex of proteins that cause metabolic changes in a cell.

metacarpal bone – one of the five long bones that form the palm of the hand; numbered 1–5, starting on the lateral (thumb) side of the hand.

metacarpophalangeal joint – articulation between the distal end of a metacarpal bone of the hand and a proximal phalanx bone of the thumb or a finger.

metaphase – second stage of mitosis (and meiosis), characterised by the linear alignment of sister chromatids in the centre of the cell.

metaphase plate – linear alignment of sister chromatids in the centre of the cell, which takes place during metaphase.

metarteriole – short vessel arising from a terminal arteriole that branches to supply a capillary bed.

metastasis – spread of cancer cells from a source to other parts of the body.

metatarsal bone – one of the five elongated bones that forms the anterior half of the foot; numbered 1–5, starting on the medial side of the foot.

metatarsophalangeal joint – articulation between a metatarsal bone of the foot and the proximal phalanx bone of a toe.

metencephalon – secondary vesicle of the embryonic brain that develops into the pons and the cerebellum.

MHC class I – found on most cells of the body, it binds to the CD8 molecule on T cells.

MHC class II – found on macrophages, dendritic cells, and B cells, it binds to CD4 molecules on T cells.

MHC polygeny – multiple MHC genes and their proteins found in body cells.

MHC polymorphism – multiple alleles for each individual MHC locus.

micelle – tiny lipid-transport compound composed of bile salts and phospholipids with a fatty acid and monoacylglyceride core.

microcirculation – blood flow through the capillaries.

microfilament – the thinnest of the cytoskeletal filaments; composed of actin subunits that function in muscle contraction and cellular structural support.

microglia – glial cell type in the CNS that serves as the resident component of the immune system.

microscopic anatomy – study of very small structures of the body using magnification.

microtubule – the thickest of the cytoskeletal filaments, composed of tubulin subunits that function in cellular movement and structural support.

microvillus – small projection of the plasma membrane of the absorptive cells of the small intestinal mucosa.

micturition – also called urination or voiding

midbrain – middle region of the adult brain that develops from the mesencephalon.

midcarpal joint – articulation between the proximal and distal rows of the carpal bones; contributes to movements of the hand at the wrist.

middle cardiac vein – vessel that parallels and drains the areas supplied by the posterior interventricular artery; drains into the great cardiac vein.

middle cerebral artery – another branch of the internal carotid artery; supplies blood to the temporal and parietal lobes of the cerebrum.

middle cranial fossa – centrally located cranial fossa that extends from the lesser wings of the sphenoid bone to the petrous ridge.

middle ear – space within the temporal bone between the ear canal and bony labyrinth where the ossicles amplify sound waves from the tympanic membrane to the oval window.

middle nasal concha – nasal concha formed by the ethmoid bone that is located between the superior and inferior conchae.

middle sacral vein – drains the sacral region and leads to the left common iliac vein.

migrating motility complex – form of peristalsis in the small intestine.

mineralocorticoids – hormones produced by the zona glomerulosa cells of the adrenal cortex that influence fluid and electrolyte balance.

mitochondrion – one of the cellular organelles bound by a double lipid bilayer that function primarily in the production of cellular energy (ATP).

mitosis – division of genetic material, during which the cell nucleus breaks down and two new, fully functional, nuclei are formed.

mitotic phase – phase of the cell cycle in which a cell undergoes mitosis.

mitotic spindle – network of microtubules, originating from centrioles, that arranges and pulls apart chromosomes during mitosis.

mitral valve – (also, left atrioventricular valve or bicuspid valve) valve located between the left atrium and ventricle; consists of two flaps of tissue.

mixing wave – unique type of peristalsis that occurs in the stomach.

modelling – process, during bone growth, by which bone is resorbed on one surface of a bone and deposited on another.

moderator band – band of myocardium covered by endocardium that arises from the inferior portion of the interventricular septum in the right ventricle and crosses to the anterior papillary muscle; contains conductile fibres that carry electrical signals followed by contraction of the heart.

molar – tooth used for crushing and grinding food.

monocytes – agranular leukocytes of the myeloid stem cell line that circulate in the bloodstream; tissue monocytes are macrophages.

monomer – smallest unit of larger molecules that are polymers.

monosaccharide – single unit or monomer of carbohydrates.

mons pubis – mound of fatty tissue located at the front of the vulva.

morula – tightly packed sphere of blastomeres that has reached the uterus but has not yet implanted itself.

motilin – hormone that initiates migrating motility complexes.

motility – movement of food through the GI tract.

motor end-plate – sarcolemma of muscle fibre at the neuromuscular junction, with receptors for the neurotransmitter acetylcholine.

motor unit – motor neuron and the group of muscle fibres it innervates.

mucosa – innermost lining of the gastrointestinal tract.

mucosa-associated lymphoid tissue (MALT) – lymphoid nodule associated with the mucosa.

mucosal barrier – protective barrier that prevents gastric juice from destroying the stomach itself.

mucous connective tissue – specialised loose connective tissue present in the umbilical cord.

mucous gland – group of cells that secrete mucous, a thick, slippery substance that keeps tissues moist and acts as a lubricant.

mucous membrane – tissue membrane that is covered by protective mucous and lines tissue exposed to the outside environment.

mucous neck cell – gastric gland cell that secretes a uniquely acidic mucus.

Müllerian duct – duct system present in the embryo that will eventually form the internal female reproductive structures.

multiaxial joint – type of diarthrosis; a joint that allows for movements within three planes (three axes).

multimodal integration area – region of the cerebral cortex in which information from more than one sensory modality is processed to arrive at higher level cortical functions such as memory, learning, or cognition.

multipolar – shape of a neuron that has multiple processes—the axon and two or more dendrites.

multipotent – describes the condition of being able to differentiate into different types of cells within a given cell lineage or small number of lineages, such as a red blood cell or white blood cell.

muscarinic receptor – type of acetylcholine receptor protein that is characterised by also binding to muscarine and is a metabotropic receptor.

muscle tissue – type of tissue that is capable of contracting and generating tension in response to stimulation; produces movement.

muscle tension – force generated by the contraction of the muscle; tension generated during isotonic contractions and isometric contractions.

muscle tone – low levels of muscle contraction that occur when a muscle is not producing movement.

muscular artery – (also, distributing artery) artery with abundant smooth muscle in the tunica media that branches to distribute blood to the arteriole network.

muscularis – muscle (skeletal or smooth) layer of the gastrointestinal tract wall.

murmur – unusual heart sound detected by auscultation; typically related to septal or valve defects.

mutation – change in the nucleotide sequence in a gene within a cell’s DNA.

myelencephalon – secondary vesicle of the embryonic brain that develops into the medulla.

myelin – layer of lipid inside some neuroglial cells that wraps around the axons of some neurons.

myelin sheath – lipid-rich layer of insulation that surrounds an axon, formed by oligodendrocytes in the CNS and Schwann cells in the PNS; facilitates the transmission of electrical signals.

myeloid stem cells – type of haemopoietic stem cell that gives rise to some formed elements, including erythrocytes, megakaryocytes that produce platelets, and a myeloblast lineage that gives rise to monocytes and three forms of granular leukocytes (neutrophils, eosinophils, and basophils).

myenteric plexus – (plexus of Auerbach) major nerve supply to gastrointestinal tract wall; controls motility.

mylohyoid line – bony ridge located along the inner (medial) surface of the mandibular body.

myoblast – muscle-forming stem cell.

myocardial conducting cells – specialised cells that transmit electrical impulses throughout the heart and trigger contraction by the myocardial contractile cells.

myocardial contractile cells – bulk of the cardiac muscle cells in the atria and ventricles that conduct impulses and contract to propel blood.

myocardium – thickest layer of the heart composed of cardiac muscle cells built upon a framework of primarily collagenous fibres and blood vessels that supply it and the nervous fibres that help to regulate it.

myocyte – muscle cells.

myofibril – long, cylindrical organelle that runs parallel within the muscle fibre and contains the sarcomeres.

myogenic mechanism – mechanism by which smooth muscle responds to stretch by contracting; an increase in blood pressure causes vasoconstriction and a decrease in blood pressure causes vasodilation so that blood flow downstream remains steady.

myogenic response – constriction or dilation in the walls of arterioles in response to pressures related to blood flow; reduces high blood flow or increases low blood flow to help maintain consistent flow to the capillary network.

myogram – instrument used to measure twitch tension.

myometrium – smooth muscle layer of uterus that allows for uterine contractions during labour and expulsion of menstrual blood.

myosin – protein that makes up most of the thick cylindrical myofilament within a sarcomere muscle fibre.

myotube – fusion of many myoblast cells.

N

nail bed – layer of epidermis upon which the nail body forms.

nail body – main keratinous plate that forms the nail.

nail cuticle – fold of epithelium that extends over the nail bed, also called the eponychium.

nail fold – fold of epithelium at that extend over the sides of the nail body, holding it in place.

nail root – part of the nail that is lodged deep in the epidermis from which the nail grows.

naïve lymphocyte – mature B or T cell that has not yet encountered antigen for the first time.

naris – (plural = nares) opening of the nostrils.

nasal bone – bone of the skull that lies under the root and bridge of the nose and is connected to the frontal and maxillary bones.

nasal cavity – opening through skull for passage of air.

nasal conchae – curved bony plates that project from the lateral walls of the nasal cavity; include the superior and middle nasal conchae, which are parts of the ethmoid bone, and the independent inferior nasal conchae bone.

nasal septum – wall composed of bone and cartilage that separates the left and right nasal cavities.

nasolacrimal canal – passage for drainage of tears that extends downward from the medial-anterior orbit to the nasal cavity, terminating behind the inferior nasal conchae.

nasopharynx – portion of the pharynx flanked by the conchae and oropharynx that serves as an airway.

natural killer (NK) cells – cytotoxic lymphocytes capable of recognising cells that do not express “self” proteins on their plasma membrane or that contain foreign or abnormal markers; provide generalised, nonspecific immunity.

navicular – tarsal bone that articulates posteriorly with the talus bone, laterally with the cuboid bone, and anteriorly with the medial, intermediate, and lateral cuneiform bones.

neck of the femur – narrowed region located inferior to the head of the femur.

neck of the radius – narrowed region immediately distal to the head of the radius.

neck of the rib – narrowed region of a rib, next to the rib head.

necrosis – accidental death of cells and tissues.

negative feedback – homeostatic mechanism that tends to stabilise an upset in the body’s physiological condition by preventing an excessive response to a stimulus, typically as the stimulus is removed.

negative inotropic factors – factors that negatively impact or lower heart contractility.

negative selection – selection against thymocytes in the thymus that react with self-antigen.

neonatal (congenital) hypothyroidism – condition characterised by cognitive deficits, short stature, and other signs and symptoms in people born to women who were iodine-deficient during pregnancy.

nephrons – functional units of the kidney that carry out all filtration and modification to produce urine; consist of renal corpuscles, proximal and distal convoluted tubules, and descending and ascending loops of Henle; drain into collecting ducts.

nerve – cord-like bundle of axons located in the peripheral nervous system that transmits sensory input and response output to and from the central nervous system.

nerve plexus – network of nerves without neuronal cell bodies included.

nervi vasorum – small nerve fibres found in arteries and veins that trigger contraction of the smooth muscle in their walls.

nervous tissue – type of tissue that is capable of sending and receiving impulses through electrochemical signals.

net filtration pressure (NFP) – force driving fluid out of the capillary and into the tissue spaces; equal to the difference of the capillary hydrostatic pressure and the blood colloidal osmotic pressure.

neural crest – tissue that detaches from the edges of the neural groove and migrates through the embryo to develop into peripheral structures of both nervous and non-nervous tissues.

neural fold – elevated edge of the neural groove.

neural groove – region of the neural plate that folds into the dorsal surface of the embryo and closes off to become the neural tube.

neural plate – thickened layer of neuroepithelium that runs longitudinally along the dorsal surface of an embryo and gives rise to nervous system tissue.

neural tube – precursor to structures of the central nervous system, formed by the invagination and separation of neuroepithelium.

neural tunic – layer of the eye that contains nervous tissue, namely the retina.

neurulation – embryonic process that establishes the central nervous system.

neuraxis – central axis to the nervous system, from the posterior to anterior ends of the neural tube; the inferior tip of the spinal cord to the anterior surface of the cerebrum.

neuroglia – supportive neural cells.

neurogenic shock – type of shock that occurs with cranial or high spinal injuries that damage the cardiovascular centres in the medulla oblongata or the nervous fibres originating from this region.

neuron – neural tissue cell that is primarily responsible for generating and propagating electrical signals into, within, and out of the nervous system.

neuropeptide – neurotransmitter type that includes protein molecules and shorter chains of amino acids.

neutralisation – inactivation of a virus by the binding of specific antibody.

neurotransmitter – signalling chemical released by nerve terminals that bind to and activate receptors on target cells.

neutrophils – granulocytes that stain with a neutral dye and are the most numerous of the leukocytes; especially active against bacteria.

nicotinic receptor – type of acetylcholine receptor protein that is characterised by also binding to nicotine and is an ionotropic receptor.

nociceptor – receptor cell that senses pain stimuli.

node of Ranvier – gap between two myelinated regions of an axon, allowing for strengthening of the electrical signal as it propagates down the axon.

nonspecific channel – channel that is not specific to one ion over another, such as a nonspecific cation channel that allows any positively charged ion across the membrane.

noradrenaline – secondary catecholamine hormone secreted by the adrenal medulla in response to short-term stress.

normal range – range of values around the set point that do not cause a reaction by the control centre.

notochord – rod-like structure along dorsal side of the early embryo; largely disappears during later development but does contribute to formation of the intervertebral discs.

nuchal ligament – expanded portion of the supraspinous ligament within the posterior neck; interconnects the spinous processes of the cervical vertebrae and attaches to the base of the skull.

nucleus – cell’s central organelle; contains the cell’s DNA.

nuclear envelope – membrane that surrounds the nucleus; consisting of a double lipid-bilayer.

nuclear pore – one of the small, protein-lined openings found scattered throughout the nuclear envelope.

nucleic acid – biological macromolecule that carries the cell’s genetic blueprint and carries instructions for the cell’s functioning.

nucleotide – monomer of nucleic acids; contains a pentose sugar, one or more phosphate groups, and a nitrogenous base.

nucleolus – small region of the nucleus that functions in ribosome synthesis.

nucleosidase – brush border enzyme that digests nucleotides.

nucleosome – unit of chromatin consisting of a DNA strand wrapped around histone proteins.

nucleus cuneatus – medullary nucleus at which first-order neurons of the dorsal column system synapse specifically from the upper body and arms.

nucleus gracilis – medullary nucleus at which first-order neurons of the dorsal column system synapse specifically from the lower body and legs.

nucleus pulposus – gel-like central region of an intervertebral disc; provides for padding, weight-bearing, and movement between adjacent vertebrae.

nutrient foramen – small opening in the middle of the external surface of the diaphysis, through which an artery enters the bone to provide nourishment.

O

obstructive shock – type of shock that occurs when a significant portion of the vascular system is blocked.

obturator foramen – large opening located in the anterior hip bone, between the pubis and ischium regions.

occipital bone – unpaired bone that forms the posterior portions of the brain case and base of the skull.

occipital condyle – paired, oval-shaped bony knobs located on the inferior skull, to either side of the foramen magnum.

occipital lobe – region of the cerebral cortex directly beneath the occipital bone of the cranium.

occipital sinus – enlarged vein that drains the occipital region near the falx cerebelli and flows into the left and right transverse sinuses, and also into the vertebral veins.

oculomotor nerve – third cranial nerve; responsible for contraction of four of the extraocular muscles, the muscle in the upper eyelid, and pupillary constriction.

odourant molecules – volatile chemicals that bind to receptor proteins in olfactory neurons to stimulate the sense of smell.

oesophagus – muscular tube that runs from the pharynx to the stomach.

oesophageal artery – branch of the thoracic aorta; supplies blood to the oesophagus.

oesophageal plexus – neuronal plexus in the wall of the oesophagus that is part of the enteric nervous system.

oesophageal vein – drains the inferior portions of the oesophagus and leads to the azygos vein.

oestrogens – class of predominantly female sex hormones important for the development and growth of the female reproductive tract, secondary sex characteristics, the female reproductive cycle, and the maintenance of pregnancy.

olecranon fossa – large depression located on the posterior side of the distal humerus; this space receives the olecranon process of the ulna when the elbow is fully extended.

olecranon process – expanded posterior and superior portions of the proximal ulna; forms the bony tip of the elbow.

olfaction – special sense responsible for smell, which has a unique, direct connection to the cerebrum.

olfactory bulb – central target of the first cranial nerve; located on the ventral surface of the frontal lobe in the cerebrum.

olfactory epithelium – region of the nasal epithelium where olfactory neurons are located.

olfactory nerve – first cranial nerve; responsible for the sense of smell.

olfactory pit – invaginated ectodermal tissue in the anterior portion of the head region of an embryo that will form the nasal cavity.

olfactory sensory neuron – receptor cell of the olfactory system, sensitive to the chemical stimuli of smell, the axons of which compose the first cranial nerve.

oligodendrocyte – neuroglial cell that produces myelin in the brain.

oligopotent – describes the condition of being more specialised than multipotency; the condition of being able to differentiate into one of a few possible cell types.

oliguria – below normal urine production of 400–500 mL/day.

omega fat – type of polyunsaturated fat that the body requires; numbering the carbon omega starts from the methyl end or the end that is farthest from the carboxylic end.

oocyte – cell that results from the division of the oogonium and undergoes meiosis I at the LH surge and meiosis II at fertilisation to become a haploid ovum.

oogenesis – process by which oogonia divide by mitosis to primary oocytes, which undergo meiosis to produce the secondary oocyte and, upon fertilisation, the ovum.

oogonia – ovarian stem cells that undergo mitosis during female foetal development to form primary oocytes.

open reduction – surgical exposure of a bone to reset a fracture.

ophthalmic artery – branch of the internal carotid artery; supplies blood to the eyes.

opposition – thumb movement that brings the tip of the thumb in contact with the tip of a finger.

opsin – protein that contains the photosensitive cofactor retinal for phototransduction.

opsonisation – enhancement of phagocytosis by the binding of antibody or antimicrobial protein.

optic canal – opening spanning between middle cranial fossa and posterior orbit.

optic chiasm – decussation point in the visual system at which medial retina fibres cross to the other side of the brain.

optic disc – spot on the retina at which RGC axons leave the eye and blood vessels of the inner retina pass.

optic nerve – second cranial nerve; responsible for visual sensation.

optic tract – name for the fibre structure containing axons from the retina posterior to the optic chiasm representing their CNS location.

orbit – bony socket that contains the eyeball and associated muscles.

oral cavity – (also, buccal cavity) mouth.

oral vestibule – part of the mouth bounded externally by the cheeks and lips, and internally by the gums and teeth.

organ – functionally distinct structure composed of two or more types of tissues.

organelle – any of several different types of membrane-enclosed specialised structures in the cell that perform specific functions for the cell.

organism – living being that has a cellular structure and that can independently perform all physiologic functions necessary for life.

organ of Corti – structure in the cochlea in which hair cells transduce movements from sound waves into electrochemical signals.

organogenesis – development of the rudimentary structures of all of an embryo’s organs from the germ layers.

organ system – group of organs that work together to carry out a particular function.

oropharynx – portion of the pharynx flanked by the nasopharynx, oral cavity, and laryngopharynx that is a passageway for both air and food.

orthopaedist – doctor who specialises in diagnosing and treating musculoskeletal disorders and injuries.

orthostatic reflex – sympathetic function that maintains blood pressure when standing to offset the increased effect of gravity.

osmoreceptor – receptor cell that senses differences in the concentrations of bodily fluids on the basis of osmotic pressure.

osmosis – diffusion of water molecules down their concentration gradient across a selectively permeable membrane.

osseous tissue – bone tissue; a hard, dense connective tissue that forms the structural elements of the skeleton.

ossicles – three small bones in the middle ear.

ossification – (also, osteogenesis) bone formation.

ossification centre – cluster of osteoblasts found in the early stages of intramembranous ossification.

osteoblast – cell responsible for forming new bone.

osteoclast – cell responsible for resorbing bone.

osteocyte – primary cell in mature bone; responsible for maintaining the matrix.

osteogenic cell – undifferentiated cell with high mitotic activity; the only bone cells that divide; they differentiate and develop into osteoblasts.

osteoid – uncalcified bone matrix secreted by osteoblasts.

osteomalacia – softening of bones due to a lack of mineralisation with calcium and phosphate; most often due to lack of vitamin D; in children, osteomalacia is termed rickets; not to be confused with osteoporosis.

osteon – (also, Haversian system) basic structural unit of compact bone; made of concentric layers of calcified matrix.

osteoporosis – disease characterised by a decrease in bone mass; occurs when the rate of bone resorption exceeds the rate of bone formation, a common occurrence as the body ages.

otolith – layer of calcium carbonate crystals located on top of the otolithic membrane.

otolithic membrane – gelatinous substance in the utricle and saccule of the inner ear that contains calcium carbonate crystals and into which the stereocilia of hair cells are embedded.

outer segment – in the eye, the section of a photoreceptor that contains opsin molecules that transduce light stimuli.

outer synaptic layer – layer in the retina at which photoreceptors connect to bipolar cells

oval window – membrane at the base of the cochlea where the stapes attaches, marking the beginning of the scala vestibuli.

ovarian artery – branch of the abdominal aorta; supplies blood to the ovary, uterine (Fallopian) tube, and uterus.

ovarian cycle – approximately 28-day cycle of changes in the ovary consisting of a follicular phase and a luteal phase.

ovarian vein – drains the ovary; the right ovarian vein leads to the inferior vena cava and the left ovarian vein leads to the left renal vein.

ovaries – female gonads that produce oocytes and sex steroid hormones (notably oestrogen and progesterone).

ovulation – release of a secondary oocyte and associated granulosa cells from an ovary.

ovum – haploid female gamete resulting from completion of meiosis II at fertilisation.

oxyhaemoglobin – molecule of haemoglobin to which oxygen is bound.

oxygen debt – amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction.

oxygen– haemoglobin dissociation curve – graph that describes the relationship of partial pressure to the binding and disassociation of oxygen to and from haem.

oxytocin – hypothalamic hormone stored in the posterior pituitary gland and important in stimulating uterine contractions in labour, milk ejection during breastfeeding, and feelings of attachment (also produced in males).

P

pacemaker – cluster of specialised myocardial cells known as the SA node that initiates the sinus rhythm.

pacesetter cell – cell that triggers action potentials in smooth muscle.

Pacinian corpuscle – (also, lamellated corpuscle) receptor in the skin that responds to vibration.

packed cell volume (PCV) – (also, haematocrit) volume percentage of erythrocytes present in a sample of centrifuged blood.

palatine bone – paired bones that form the posterior quarter of the hard palate and a small area in floor of the orbit.

palatine process – medial projection from the maxilla bone that forms the anterior three quarters of the hard palate.

palatine tonsil – one of the paired structures composed of lymphoid tissue located anterior to the uvula at the roof of isthmus of the fauces.

palatoglossal arch – muscular fold that extends from the lateral side of the soft palate to the base of the tongue.

palatopharyngeal arch – muscular fold that extends from the lateral side of the soft palate to the side of the pharynx.

palmar arches – superficial and deep arches formed from anastomoses of the radial and ulnar arteries; supply blood to the hand and digital arteries.

palmar venous arches – drain the hand and digits, and feed into the radial and ulnar veins.

palpebral conjunctiva – membrane attached to the inner surface of the eyelids that covers the anterior surface of the cornea.

pancreas – accessory digestive organ that secretes pancreatic secretion.

pancreatic amylase – enzyme secreted by the pancreas that completes the chemical digestion of carbohydrates in the small intestine.

pancreatic islets – specialised clusters of pancreatic cells that have endocrine functions; also called islets of Langerhans.

pancreatic lipase – enzyme secreted by the pancreas that participates in lipid digestion.

pancreatic nuclease – enzyme secreted by the pancreas that participates in nucleic acid digestion.

pancreatic secretion – secretion of the pancreas containing digestive enzymes and bicarbonate.

papilla – for gustation, a bump-like projection on the surface of the tongue that contains taste buds.

papillary layer – superficial layer of the dermis, made of loose, areolar connective tissue.

papillary muscle – extension of the myocardium in the ventricles to which the chordae tendineae attach.

paracrine – chemical signal that elicits a response in neighbouring cells; also called paracrine factor.

paranasal sinus – one of the cavities within the skull that is connected to the conchae that serve to warm and humidify incoming air, produce mucus, and lighten the weight of the skull; consists of frontal, maxillary, sphenoidal, and ethmoidal sinuses.

parathyroid glands – small, round glands embedded in the posterior thyroid gland that produce parathyroid hormone (PTH).

parathyroid hormone (PTH) – peptide hormone produced and secreted by the parathyroid glands in response to low blood calcium levels.

paravertebral ganglia – autonomic ganglia superior to the sympathetic chain ganglia.

parenchyma – functional cells of a gland or organ, in contrast with the supportive or connective tissue of a gland or organ.

parietal bone – paired bones that form the upper, lateral sides of the skull.

parietal branches – (also, somatic branches) group of arterial branches of the thoracic aorta; includes those that supply blood to the thoracic cavity, vertebral column, and the superior surface of the diaphragm.

parietal cell – gastric gland cell that secretes hydrochloric acid and intrinsic factor.

parietal lobe – region of the cerebral cortex directly beneath the parietal bone of the cranium.

parietal pleura – outermost layer of the pleura that connects to the thoracic wall, mediastinum, and diaphragm.

parieto-occipital sulcus – groove in the cerebral cortex representing the border between the parietal and occipital cortices.

parotid gland – one of a pair of major salivary glands located inferior and anterior to the ears.

partial pressure – force exerted by each gas in a mixture of gases.

partial thickness burns – partial-thickness burn that injures the epidermis and a portion of the dermis.

passive immunity – transfer of immunity to a pathogen to an individual that lacks immunity to this pathogen usually by the injection of antibodies.

passive transport – form of transport across the cell membrane that does not require input of cellular energy.

patella – kneecap; the largest sesamoid bone of the body; articulates with the distal femur.

patellar ligament – ligament spanning from the patella to the anterior tibia; serves as the final attachment for the quadriceps femoris muscle.

patellar surface – smooth groove located on the anterior side of the distal femur, between the medial and lateral condyles; site of articulation for the patella.

pattern recognition receptor (PRR) – leukocyte receptor that binds to specific cell wall components of different bacterial species.

pectinate line – horizontal line that runs like a ring, perpendicular to the inferior margins of the anal sinuses.

pectinate muscles – muscular ridges seen on the anterior surface of the right atrium.

pectineal line – narrow ridge located on the superior surface of the superior pubic ramus.

pectoral girdle – shoulder girdle; the set of bones, consisting of the scapula and clavicle, which attaches each upper limb to the axial skeleton.

pedicels – finger-like projections of podocytes surrounding glomerular capillaries; interdigitate to form a filtration membrane.

pedicle – portion of the vertebral arch that extends from the vertebral body to the transverse process.

pelvic brim – pelvic inlet; the dividing line between the greater and lesser pelvic regions; formed by the superior margin of the pubic symphysis, the pectineal lines of each pubis, the arcuate lines of each ilium, and the sacral promontory.

pelvic girdle – hip girdle; consists of a single hip bone, which attaches a lower limb to the sacrum of the axial skeleton.

pelvic inlet – pelvic brim.

pelvic outlet – inferior opening of the lesser pelvis; formed by the inferior margin of the pubic symphysis, right and left ischiopubic rami and sacrotuberous ligaments, and the tip of the coccyx.

pelvis – ring of bone consisting of the right and left hip bones, the sacrum, and the coccyx.

penis – male organ of copulation.

pepsinogen – inactive form of pepsin.

peptide bond – bond formed between two amino acids by a dehydration reaction.

perforating canal – (also, Volkmann’s canal) channel that branches off from the central canal and houses vessels and nerves that extend to the periosteum and endosteum.

perforin – molecule in NK cell and cytotoxic T cell granules that form pores in the membrane of a target cell.

perfusion – distribution of blood into the capillaries so the tissues can be supplied.

pericardial artery – branch of the thoracic aorta; supplies blood to the pericardium.

pericardial cavity – cavity surrounding the heart filled with a lubricating serous fluid that reduces friction as the heart contracts.

pericardial sac – (also, pericardium) membrane that separates the heart from other mediastinal structures; consists of two distinct, fused sublayers: the fibrous pericardium and the parietal pericardium.

pericardium – (also, pericardial sac) membrane that separates the heart from other mediastinal structures; consists of two distinct, fused sublayers: the fibrous pericardium and the parietal pericardium.

perichondrium – membrane that covers cartilage.

pericyte – stem cell that regenerates smooth muscle cells.

perimetrium – outer epithelial layer of uterine wall.

perimysium – connective tissue that bundles skeletal muscle fibres into fascicles within a skeletal muscle.

perineurium – layer of connective tissue surrounding fascicles within a nerve.

periodontal ligament – band of dense connective tissue that anchors the root of a tooth into the bony jaw socket.

peripheral chemoreceptor – one of the specialised receptors located in the aortic arch and carotid arteries that sense changes in pH, carbon dioxide, or oxygen blood levels.

peripheral nervous system (PNS) – anatomical division of the nervous system that is largely outside the cranial and vertebral cavities, namely all parts except the brain and spinal cord.

peripheral protein – membrane-associated protein that does not span the width of the lipid bilayer, but is attached peripherally to integral proteins, membrane lipids, or other components of the membrane.

peripheral tolerance – mature B cell made tolerant by lack of T cell help.

periosteum – fibrous membrane covering the outer surface of bone and continuous with ligaments.

peristalsis – muscular contractions and relaxations that propel food through the GI tract.

peritoneum – serous membrane that lines the abdominopelvic cavity and covers the organs found there.

peritubular capillaries – second capillary bed of the renal portal system; surround the proximal and distal convoluted tubules; associated with the vasa recta

permanent tooth – one of 32 adult teeth.

peroxisome – membrane-bound organelle that contains enzymes primarily responsible for detoxifying harmful substances.

perpendicular plate of the ethmoid bone – downward, midline extension of the ethmoid bone that forms the superior portion of the nasal septum.

petrosal sinus – enlarged vein that receives blood from the cavernous sinus and flows into the internal jugular vein.

petrous ridge – petrous portion of the temporal bone that forms a large, triangular ridge in the floor of the cranial cavity, separating the middle and posterior cranial fossae; houses the middle and inner ear structures.

phagocytosis – endocytosis of large particles.

phalanx bone of the foot – (plural = phalanges) one of the 14 bones that form the toes; these include the proximal and distal phalanges of the big toe, and the proximal, middle, and distal phalanx bones of toes two through five.

phalanx bone of the hand – (plural = phalanges) one of the 14 bones that form the thumb and fingers; these include the proximal and distal phalanges of the thumb, and the proximal, middle, and distal phalanx bones of the fingers two through five.

pharyngeal tonsil – structure composed of lymphoid tissue located in the nasopharynx.

pharynx – region of the conducting zone that forms a tube of skeletal muscle lined with respiratory epithelium; located between the nasal conchae and the oesophagus and trachea.

philtrum – concave surface of the face that connects the apex of the nose to the top lip.

phosphatase – brush border enzyme that digests nucleotides.

phosphodiester – linkage covalent chemical bond that holds together the polynucleotide chains with a phosphate group linking neighbouring nucleotides’ two pentose sugars.

phosphodiesterase (PDE) – cytosolic enzyme that deactivates and degrades cAMP.

photoisomerisation – chemical change in the retinal molecule that alters the bonding so that it switches from the 11-cis-retinal isomer to the all-trans-retinal isomer.

phosphorylation cascade – signalling event in which multiple protein kinases phosphorylate the next protein substrate by transferring a phosphate group from ATP to the protein.

photon – individual “packet” of light.

photoreceptor – receptor cell specialised to respond to light stimuli.

phrenic nerve – systemic nerve from the cervical plexus that enervates the diaphragm.

phrenic vein – drains the diaphragm; the right phrenic vein flows into the inferior vena cava and the left phrenic vein leads to the left renal vein.

physiology – science that studies the chemistry, biochemistry, and physics of the body’s functions.

physiological sphincter – sphincter consisting of circular smooth muscle indistinguishable from adjacent muscle but possessing differential innervations, permitting its function as a sphincter; structurally weak

pia mater – thin, innermost membrane of the meninges that directly covers the surface of the CNS.

pineal gland – endocrine gland that secretes melatonin, which is important in regulating the sleep-wake cycle.

pinealocyte – cell of the pineal gland that produces and secretes the hormone melatonin.

pinocytosis – endocytosis of fluid.

pisiform – from the lateral side, the fourth of the four proximal carpal bones; articulates with the anterior surface of the triquetrum.

pituitary dwarfism – disorder in children caused when abnormally low levels of GH result in growth retardatio.

pituitary gland – bean-sized organ suspended from the hypothalamus that produces, stores, and secretes hormones in response to hypothalamic stimulation (also called hypophysis).

pivot joint – synovial joint at which the rounded portion of a bone rotates within a ring formed by a ligament and an articulating bone; functionally classified as uniaxial joint.

placenta – organ that forms during pregnancy to nourish the developing foetus; also regulates waste and gas exchange between mother and foetus.

placenta previa – low placement of foetus within uterus causes placenta to partially or completely cover the opening of the cervix as it grows.

placentation – formation of the placenta; complete by weeks 14–16 of pregnancy.

plane – imaginary two-dimensional surface that passes through the body.

plane joint – synovial joint formed between the flattened articulating surfaces of adjacent bones; functionally classified as a multiaxial joint.

plantar arch – formed from the anastomosis of the dorsalis pedis artery and medial and plantar arteries; branches supply the distal portions of the foot and digits.

plantar flexion – foot movement at the ankle in which the heel is lifted off of the ground.

plantar veins – drain the foot and lead to the plantar venous arch.

plantar venous arch – formed from the plantar veins; leads to the anterior and posterior tibial veins through anastomoses.

plasma – in blood, the liquid extracellular matrix composed mostly of water that circulates the formed elements and dissolved materials throughout the cardiovascular system.

plasma cell – differentiated B cell that is actively secreting antibody.

plasma osmolality – ratio of solutes to a volume of solvent in the plasma; plasma osmolality reflects a person’s state of hydration.

plasmin – plasma blood protein active in fibrinolysis.

platelets – (also, thrombocytes) one of the formed elements of blood that consists of cell fragments broken off from megakaryocytes.

platelet plug – adhesion and aggregation of platelets at the site of blood vessel injury.

pleura – serous membrane that lines the pleural cavity and covers the lungs.

pleural cavity – space between the visceral and parietal pleurae.

pleural fluid – substance that acts as a lubricant for the visceral and parietal layers of the pleura during the movement of breathing.

plexus – network of nerves or nervous tissue.

pluripotent – describes the condition of being able to differentiate into a large variety of cell types.

pluripotent stem cell – stem cell that derives from totipotent stem cells and is capable of differentiating into many, but not all, cell types.

pneumotaxic centre – network of neurons within the pons that inhibit the activity of the neurons in the dorsal respiratory group; controls rate of breathing.

podocytes – cells forming finger-like processes; form the visceral layer of Bowman’s capsule; pedicels of the podocytes interdigitate to form a filtration membrane.

polar body – smaller cell produced during the process of meiosis in oogenesis.

pollex – (also, thumb) digit 1 of the hand.

polyclonal response – response by multiple clones to a complex antigen with many determinants.

polycythaemia – elevated level of haemoglobin and RBC, whether adaptive or pathological.

polymer – chain of monomer residues that covalent bonds link; polymerisation is the process of polymer formation from monomers by condensation.

polymorphonuclear – having a lobed nucleus, as seen in some leukocytes.

polynucleotide – long chain of nucleotides.

polypeptide – chain of amino acids linked by peptide bonds.

polyribosome – simultaneous translation of a single mRNA transcript by multiple ribosomes.

polysaccharide – long chain of monosaccharides; may be branched or unbranched.

polyspermy – penetration of an oocyte by more than one sperm.

polyuria – urine production in excess of 2.5 L/day; may be caused by diabetes insipidus, diabetes mellitus, or excessive use of diuretics.

popliteal artery – continuation of the femoral artery posterior to the knee; branches into the anterior and posterior tibial arteries.

popliteal vein – continuation of the femoral vein behind the knee; drains the region behind the knee and forms from the fusion of the fibular and anterior and posterior tibial veins.

porta hepatis – “gateway to the liver” where the hepatic artery and hepatic portal vein enter the liver.

portal triad – bile duct, hepatic artery branch, and hepatic portal vein branch.

postcentral gyrus – ridge just posterior to the central sulcus, in the parietal lobe, where somatosensory processing initially takes place in the cerebrum.

posterior – describes the back or direction toward the back of the body; also referred to as dorsal.

posterior arch – posterior portion of the ring-like C1 (atlas) vertebra.

posterior cardiac vein – vessel that parallels and drains the areas supplied by the marginal artery branch of the circumflex artery; drains into the great cardiac vein.

posterior cavity – posterior body cavity that houses the brain and spinal cord; also referred to as dorsal cavity.

posterior cerebral artery – branch of the basilar artery that forms a portion of the posterior segment of the arterial circle; supplies blood to the posterior portion of the cerebrum and brain stem.

posterior columns – white matter of the spinal cord that lies between the posterior horns of the grey matter, sometimes referred to as the dorsal column; composed of axons of ascending tracts that carry sensory information up to the brain.

posterior communicating artery – branch of the posterior cerebral artery that forms part of the posterior portion of the arterial circle; supplies blood to the brain.

posterior cranial fossa – deepest and most posterior cranial fossa; extends from the petrous ridge to the occipital bone.

posterior cruciate ligament – intracapsular ligament of the knee; extends from the posterior, superior surface of the tibia to the inner aspect of the medial condyle of the femur; prevents anterior displacement of the femur when the knee is flexed and weight bearing.

posterior horn – grey matter region of the spinal cord in which sensory input arrives, sometimes referred to as the dorsal horn.

posterior inferior iliac spine – small, bony projection located at the inferior margin of the auricular surface on the posterior ilium.

posterior interventricular artery – (also, posterior descending artery) branch of the right coronary artery that runs along the posterior portion of the interventricular sulcus toward the apex of the heart and gives rise to branches that supply the interventricular septum and portions of both ventricles.

posterior interventricular sulcus – sulcus located between the left and right ventricles on the anterior surface of the heart.

posterior longitudinal ligament – ligament that runs the length of the vertebral column, uniting the posterior sides of the vertebral bodies.

posterior median sulcus – midline feature of the posterior spinal cord, marking the separation between right and left sides of the cord.

posterior (dorsal) sacral foramen – one of the series of paired openings located on the posterior (dorsal) side of the sacrum.

posterior sacroiliac ligament – strong ligament spanning the sacrum and ilium of the hip bone that supports the posterior side of the sacroiliac joint.

posterior superior iliac spine – rounded, posterior end of the iliac crest.

posterior talofibular ligament – intrinsic ligament located on the lateral side of the ankle joint, between the talus bone and lateral malleolus of the fibula; supports the talus at the talocrural joint and resists excess inversion of the foot.

posterior tibial artery – branch from the popliteal artery that gives rise to the fibular or peroneal artery; supplies blood to the posterior tibial region.

posterior tibial vein – forms from the dorsal venous arch; drains the area near the posterior surface of the tibia and leads to the popliteal vein.

posterolateral sulcus – feature of the posterior spinal cord marking the entry of posterior nerve roots and the separation between the posterior and lateral columns of the white matter.

positive chemotaxis – process in which a cell is attracted to move in the direction of chemical stimuli.

positive feedback – mechanism that intensifies a change in the body’s physiological condition in response to a stimulus.

positive inotropic factors – factors that positively impact or increase heart contractility.

positive selection – selection of thymocytes within the thymus that interact with self, but not non-self, MHC molecules.

postsynaptic potential (PSP) – graded potential in the postsynaptic membrane caused by the binding of neurotransmitter to protein receptors.

power stroke – action of myosin pulling actin inward (toward the M line).

precapillary sphincters – circular rings of smooth muscle that surround the entrance to a capillary and regulate blood flow into that capillary.

precentral gyrus – primary motor cortex located in the frontal lobe of the cerebral cortex.

precentral gyrus of the frontal cortex – region of the cerebral cortex responsible for generating motor commands, where the upper motor neuron cell body is located.

prefrontal lobe – specific region of the frontal lobe anterior to the more specific motor function areas, which can be related to the early planning of movements and intentions to the point of being personality-type functions.

preload – (also, end diastolic volume) amount of blood in the ventricles at the end of atrial systole just prior to ventricular contraction.

premolar – (also, bicuspid) transitional tooth used for mastication, crushing, and grinding food.

premotor area – region of the frontal lobe responsible for planning movements that will be executed through the primary motor cortex.

premotor cortex – cortical area anterior to the primary motor cortex that is responsible for planning movements.

prepotential depolarisation – (also, spontaneous depolarisation) mechanism that accounts for the autorhythmic property of cardiac muscle; the membrane potential increases as sodium ions diffuse through the always-open sodium ion channels and causes the electrical potential to rise.

prepuce – (also, foreskin) flap of skin that forms a collar around, and thus protects and lubricates, the glans penis; also referred as the foreskin.

prevertebral ganglia – autonomic ganglia that are anterior to the vertebral column and functionally related to the sympathetic chain ganglia.

primary adaptive response – immune system’s response to the first exposure to a pathogen.

primary curve – anteriorly concave curvatures of the thoracic and sacrococcygeal regions that are retained from the original foetal curvature of the vertebral column.

primary follicles – ovarian follicles with a primary oocyte and one layer of cuboidal granulosa cells.

primary lymphoid organ – site where lymphocytes mature and proliferate; red bone marrow and thymus gland.

primary ossification centre – region, deep in the periosteal collar, where bone development starts during endochondral ossification.

primary sensory cortex – region of the cerebral cortex that initially receives sensory input from an ascending pathway from the thalamus and begins the processing that will result in conscious perception of that modality.

primary structure – linear sequence of amino acids in a protein.

primary union – condition of a wound where the wound edges are close enough to be brought together and fastened if necessary, allowing quicker and more thorough healing.

primary vesicle – initial enlargements of the anterior neural tube during embryonic development that develop into the forebrain, midbrain, and hindbrain.

primitive atrium – portion of the primitive heart tube that eventually becomes the anterior portions of both the right and left atria, and the two auricles.

primitive heart tube – singular tubular structure that forms from the fusion of the two endocardial tubes.

primitive streak – indentation along the dorsal surface of the epiblast through which cells migrate to form the endoderm and mesoderm during gastrulation.

primitive ventricle – portion of the primitive heart tube that eventually forms the left ventricle.

primordial follicles – least developed ovarian follicles that consist of a single oocyte and a single layer of flat (squamous) granulosa cells.

principal cell – found in collecting ducts and possess channels for the recovery or loss of sodium and potassium; under the control of aldosterone; also have aquaporin channels under ADH control to regulate recovery of water.

process – in cells, an extension of a cell body; in the case of neurons, this includes the axon and dendrites.

progesterone – predominantly female sex hormone important in regulating the female reproductive cycle and the maintenance of pregnancy.

projection – bone markings where part of the surface sticks out above the rest of the surface, where tendons and ligaments attach.

prolactin (PRL) – anterior pituitary hormone that promotes development of the mammary glands and the production of breast milk.

proliferative phase – phase of the menstrual cycle in which the endometrium proliferates.

proliferative zone – region of the epiphyseal plate that makes new chondrocytes to replace those that die at the diaphyseal end of the plate and contributes to longitudinal growth of the epiphyseal plate.

promoter – region of DNA that signals transcription to begin at that site within the gene.

pronated position – forearm position in which the palm faces backward.

pronation – forearm motion that moves the palm of the hand from the palm forward to the palm backward position.

prone – face down.

propagation – movement of an action potential along the length of an axon.

prophase – first stage of mitosis (and meiosis), characterised by breakdown of the nuclear envelope and condensing of the chromatin to form chromosomes.

proprioception – general sensory perceptions providing information about location and movement of body parts; the “sense of the self”.

proprioceptor – receptor cell that senses changes in the position and kinaesthetic aspects of the body.

propulsion – voluntary process of swallowing and the involuntary process of peristalsis that moves food through the digestive tract.

prosencephalon – primary vesicle of the embryonic brain that develops into the forebrain, which includes the cerebrum and diencephalon.

prostate gland – doughnut-shaped gland at the base of the bladder surrounding the urethra and contributing fluid to semen during ejaculation.

protein – biological macromolecule comprised of one or more amino acid chains.

protein kinase – enzyme that initiates a phosphorylation cascade upon activation.

proteome – full complement of proteins produced by a cell (determined by the cell’s specific gene expression).

protraction – anterior motion of the scapula or mandible.

proximal – describes a position nearer to the point of attachment or the trunk of the body.

proximal convoluted tubules (PCTs) – tortuous tubules receiving filtrate from Bowman’s capsule; most active part of the nephron in reabsorption and secretion.

proximal radioulnar joint – articulation formed by the radial notch of the ulna and the head of the radius.

proximal tibiofibular joint – articulation between the head of the fibula and the inferior aspect of the lateral condyle of the tibia.

pseudostratified columnar epithelium – tissue that consists of a single layer of irregularly shaped and sized cells that give the appearance of multiple layers; found in ducts of certain glands and the upper respiratory tract.

psychoneuroimmunology – study of the connections between the immune, nervous, and endocrine systems.

pterion – H-shaped suture junction region that unites the frontal, parietal, temporal, and sphenoid bones on the lateral side of the skull.

puberty – life stage during which a male or female adolescent becomes anatomically and physiologically capable of reproduction.

pubic arch – bony structure formed by the pubic symphysis, and the bodies and inferior pubic rami of the right and left pubic bones.

pubic body – enlarged, medial portion of the pubis region of the hip bone.

pubic symphysis – joint formed by the articulation between the pubic bodies of the right and left hip bones.

pubic tubercle – small bump located on the superior aspect of the pubic body.

pubis – anterior portion of the hip bone.

pubofemoral ligament – intrinsic ligament spanning from the pubis of the hip bone to the femur, on the anterior-inferior aspect of the hip joint.

pulmonary arteries – left and right branches of the pulmonary trunk that carry deoxygenated blood from the heart to each of the lungs.

pulmonary capillaries – capillaries surrounding the alveoli of the lungs where gas exchange occurs: carbon dioxide exits the blood and oxygen enters.

pulmonary circuit – blood flow to and from the lungs.

pulmonary plexus – network of autonomic nervous system fibres found near the hilum of the lung.

pulmonary surfactant – substance composed of phospholipids and proteins that reduces the surface tension of the alveoli; made by type II alveolar cells.

pulmonary trunk – large arterial vessel that carries blood ejected from the right ventricle; divides into the left and right pulmonary arteries.

pulmonary valve – (also, pulmonary semilunar valve, the pulmonic valve, or the right semilunar valve) valve at the base of the pulmonary trunk that prevents backflow of blood into the right ventricle; consists of three flaps.

pulmonary veins – veins that carry highly oxygenated blood into the left atrium, which pumps the blood into the left ventricle, which in turn pumps oxygenated blood into the aorta and to the many branches of the systemic circuit.

pulmonary ventilation – exchange of gases between the lungs and the atmosphere; breathing.

pulp cavity – deepest portion of a tooth, containing nerve endings and blood vessels.

pulse – alternating expansion and recoil of an artery as blood moves through the vessel; an indicator of heart rate.

pulse pressure – difference between the systolic and diastolic pressures.

pupil – open hole at the centre of the iris that light passes through into the eye.

purine – type of nitrogenous base in DNA and RNA; adenine and guanine are purines.

Purkinje fibres – specialised myocardial conduction fibres that arise from the bundle branches and spread the impulse to the myocardial contraction fibres of the ventricles.

putamen – nucleus deep in the cerebrum that is part of the basal nuclei; along with the caudate, it is part of the striatum.

P wave – component of the electrocardiogram that represents the depolarisation of the atria.

pyloric antrum – wider, more superior part of the pylorus.

pyloric canal – narrow, more inferior part of the pylorus.

pyloric sphincter – sphincter that controls stomach emptying.

pylorus – lower, funnel-shaped part of the stomach that is continuous with the duodenum.

pyramidal decussation – location at which corticospinal tract fibres cross the midline and segregate into the anterior and lateral divisions of the pathway.

pyramids – segment of the descending motor pathway that travels in the anterior position of the medulla.

pyruvic acid – product of glycolysis that can be used in aerobic respiration or converted to lactic acid.

Q

quaternary structure – association of discrete polypeptide subunits in a protein.

quickening – foetal movements that are strong enough to be felt by the mother

quiet breathing – (also, eupnoea) mode of breathing that occurs at rest and does not require the cognitive thought of the individual.

QRS complex – component of the electrocardiogram that represents the depolarisation of the ventricles and includes, as a component, the repolarisation of the atria.

R

radial artery – formed at the bifurcation of the brachial artery; parallels the radius; gives off smaller branches until it reaches the carpal region where it fuses with the ulnar artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region.

radial collateral ligament – intrinsic ligament on the lateral side of the elbow joint; runs from the lateral epicondyle of humerus to merge with the annular ligament.

radial fossa (anatomical snuff box)– small depression located on the anterior humerus above the capitulum; this space receives the head of the radius when the elbow is maximally flexed sometimes also known as the anatomical snuff box.

radial nerve – systemic nerve of the arm, the distal component of which is located near the radial bone.

radial notch of the ulna – small, smooth area on the lateral side of the proximal ulna; articulates with the head of the radius as part of the proximal radioulnar joint.

radial tuberosity – oval-shaped, roughened protuberance located on the medial side of the proximal radius.

radial vein – parallels the radius and radial artery; arises from the palmar venous arches and leads to the brachial vein.

radiocarpal joint – wrist joint, located between the forearm and hand regions of the upper limb; articulation formed proximally by the distal end of the radius and the fibrocartilaginous pad that unites the distal radius and ulna bone, and distally by the scaphoid, lunate, and triquetrum carpal bones.

radius – bone located on the lateral side of the forearm.

ramus of the mandible – vertical portion of the mandible.

reabsorption – in the cardiovascular system, the movement of material from the interstitial fluid into the capillaries.

reactive oxygen species (ROS) – a group of extremely reactive peroxides and oxygen-containing radicals that may contribute to cellular damage.

receptor – protein molecule that contains a binding site for another specific molecule (called a ligand).

receptor cell – cell that transduces environmental stimuli into neural signals.

receptor-mediated endocytosis – endocytosis of ligands attached to membrane-bound receptors.

receptor potential – graded potential in a specialised sensory cell that directly causes the release of neurotransmitter without an intervening action potential.

recruitment – increase in the number of motor units involved in contraction.

rectal valve – one of three transverse folds in the rectum where faeces is separated from flatus.

rectum – part of the large intestine between the sigmoid colon and anal canal.

red blood cells (RBCs) – (also, erythrocytes) one of the formed elements of blood that transports oxygen.

red marrow – connective tissue in the interior cavity of a bone where haematopoiesis takes place.

red nucleus – midbrain nucleus that sends corrective commands to the spinal cord along the rubrospinal tract, based on disparity between an original command and the sensory feedback from movement.

refractory period – time after the initiation of an action potential when another action potential cannot be generated.

regional anatomy – study of the structures that contribute to specific body regions.

regulatory T cells (Treg) – (also, suppressor T cells) class of CD4 T cells that regulates other T cell responses.

relative refractory period – time during the refractory period when a new action potential can only be initiated by a stronger stimulus than the current action potential because voltage-gated K⁺ channels are not closed.

relaxation phase – period after twitch contraction when tension decreases.

remodelling – process by which osteoclasts resorb old or damaged bone at the same time as and on the same surface where osteoblasts form new bone to replace that which is resorbed.

renal artery – branch of the abdominal aorta; supplies each kidney.

renal columns – extensions of the renal cortex into the renal medulla; separates the renal pyramids; contains blood vessels and connective tissues.

renal corpuscle – consists of the glomerulus and Bowman’s capsule.

renal cortex – outer part of kidney containing all the nephrons; some nephrons have loops of Henle extending into the medulla.

renal fat pad – adipose tissue between the renal fascia and the renal capsule that provides protective cushioning to the kidney.

renal hilum – recessed medial area of the kidney through which the renal artery, renal vein, ureters, lymphatics, and nerves pass.

renal papillae – medullary area of the renal pyramids where collecting ducts empty urine into the minor calyces.

renal pyramids – six to eight cone-shaped tissues in the medulla of the kidney containing collecting ducts and the loops of Henle of juxtamedullary nephrons.

renal vein – largest vein entering the inferior vena cava; drains the kidneys and leads to the inferior vena cava.

renin – enzyme produced by juxtaglomerular cells in response to decreased blood pressure or sympathetic nervous activity; catalyses the conversion of angiotensinogen into angiotensin I.

repolarisation – return of the membrane potential to its normally negative voltage at the end of the action potential.

reposition – movement of the thumb from opposition back to the anatomical position (next to index finger).

reserve zone – region of the epiphyseal plate that anchors the plate to the osseous tissue of the epiphysis.

residual volume (RV) – amount of air that remains in the lungs after maximum exhalation.

resistance – any condition or parameter that slows or counteracts the flow of blood.

respiratory acidosis – condition wherein an excess of carbonic acid or CO2 causes the blood to be overly acidic.

respiratory alkalosis – condition wherein a deficiency of carbonic acid/CO2 levels causes the blood to be overly alkaline.

respiratory bronchiole – specific type of bronchiole that leads to alveolar sacs.

respiratory cycle – one sequence of inspiration and expiration.

respiratory epithelium – ciliated lining of much of the conducting zone that is specialised to remove debris and pathogens, and produce mucus.

respiratory membrane – alveolar and capillary wall together, which form an air-blood barrier that facilitates the simple diffusion of gases.

respiratory pump – increase in the volume of the thorax during inhalation that decreases air pressure, enabling venous blood to flow into the thoracic region, then exhalation increases pressure, moving blood into the atria.

respiratory rate – total number of breaths taken each minute.

respiratory volume – varying amounts of air within the lung at a given time.

respiratory zone – includes structures of the respiratory system that are directly involved in gas exchange.

response – nervous system function that causes a target tissue (muscle or gland) to produce an event as a consequence to stimuli.

resting membrane potential – the difference in voltage measured across a cell membrane under steady-state conditions, typically -70 mV.

reticular fibres – fine fibrous protein, made of collagen subunits, which cross-link to form supporting “nets” within connective tissue.

reticular formation – diffuse region of grey matter throughout the brain stem that regulates sleep, wakefulness, and states of consciousness.

reticular lamina – matrix containing collagen and elastin secreted by connective tissue; a component of the basement membrane.

reticular layer – deeper layer of the dermis; it has a reticulated appearance due to the presence of abundant collagen and elastin fibres.

reticular tissue – type of loose connective tissue that provides a supportive framework to soft organs, such as lymphatic tissue, spleen, and the liver.

reticulocyte – immature erythrocyte that may still contain fragments of ribosomal RNA.

reticuloendothelial cell – (also, Kupffer cell) phagocyte in hepatic sinusoids that filters out material from venous blood from the gastrointestinal tract.

reticulospinal tract – extrapyramidal connections between the brain stem and spinal cord that modulate movement, contribute to posture, and regulate muscle tone.

retina – nervous tissue of the eye at which phototransduction takes place.

retinal – cofactor in an opsin molecule that undergoes a biochemical change when struck by a photon (pronounced with a stress on the last syllable).

retinal ganglion cell (RGC) – neuron of the retina that projects along the second cranial nerve.

retraction – posterior motion of the scapula or mandible.

retroperitoneal– outside the peritoneal cavity; in the case of the kidney and ureters, between the parietal peritoneum and the abdominal wall.

Rh blood group – blood-type classification based on the presence or absence of the antigen Rh(D) on the erythrocyte membrane surface.

rhodopsin – photopigment molecule found in the rod photoreceptors.

rhombencephalon – primary vesicle of the embryonic brain that develops into the hindbrain, which includes the pons, cerebellum, and medulla.

ribonuclease – pancreatic enzyme that digests RNA.

ribonucleic acid (RNA) – single-stranded, often internally base paired, molecule that is involved in protein synthesis.

ribosome – cellular organelle that functions in protein synthesis.

ribosomal RNA (rRNA) – RNA that makes up the subunits of a ribosome.

ribs – thin, curved bones of the chest wall.

rickets – disease in children caused by vitamin D deficiency, which leads to the weakening of bones.

right atrioventricular valve – (also, tricuspid valve) valve located between the right atrium and ventricle; consists of three flaps of tissue.

right colic flexure – (also, hepatic flexure) point, at the inferior surface of the liver, where the ascending colon turns abruptly to the left.

right gastric artery – branch of the common hepatic artery; supplies blood to the stomach.

right lymphatic duct – drains lymph fluid from the upper right side of body into the right subclavian vein.

RNA polymerase – enzyme that unwinds DNA and then adds new nucleotides to a growing strand of RNA for the transcription phase of protein synthesis.

rod photoreceptor – one of the two types of retinal receptor cell that is specialised for low-light vision.

root – region of the external nose between the eyebrows.

root – portion of a tooth embedded in the alveolar processes beneath the gum line.

rotation – movement of a bone around a central axis (atlantoaxial joint) or around its long axis (proximal radioulnar joint; shoulder or hip joint); twisting of the vertebral column resulting from the summation of small motions between adjacent vertebrae.

rotator cuff – strong connective tissue structure formed by the fusion of four rotator cuff muscle tendons to the articular capsule of the shoulder joint; surrounds and supports superior, anterior, lateral, and posterior sides of the humeral head.

round window – membrane that marks the end of the scala tympani.

rubrospinal tract – descending motor control pathway, originating in the red nucleus, that mediates control of the limbs based on cerebellar processing.

ruga – fold of gastrointestinal tract mucosa and submucosa in the empty stomach and other organs.

rugae – (of the vagina) folds of skin in the vagina that allow it to stretch during intercourse and childbirth.

S

saccharolytic fermentation – anaerobic decomposition of carbohydrates.

saccule – structure of the inner ear responsible for transducing linear acceleration in the vertical plane.

sacral canal – bony tunnel that runs through the sacrum.

sacral foramina – series of paired openings for nerve exit located on both the anterior (ventral) and posterior (dorsal) aspects of the sacrum.

sacral hiatus – inferior opening and termination of the sacral canal.

sacral micturition centre – group of neurons in the sacral region of the spinal cord that controls urination; acts reflexively unless its action is modified by higher brain centres to allow voluntary urination.

sacral plexus – nerve plexus associated with the lower lumbar and sacral spinal nerves.

sacral promontory – anterior lip of the base (superior end) of the sacrum.

sacrococcygeal curve – anteriorly concave curvature formed by the sacrum and coccyx; a primary curve of the vertebral column.

sacroiliac joint – joint formed by the articulation between the auricular surfaces of the sacrum and ilium.

sacrospinous ligament – ligament that spans the sacrum to the ischial spine of the hip bone.

sacrotuberous ligament – ligament that spans the sacrum to the ischial tuberosity of the hip bone.

sacrum – single bone located near the inferior end of the adult vertebral column that is formed by the fusion of five sacral vertebrae; forms the posterior portion of the pelvis.

saddle joint – synovial joint in which the articulating ends of both bones are convex and concave in shape, such as at the first carpometacarpal joint at the base of the thumb; functionally classified as a biaxial joint.

sagittal plane – two-dimensional, vertical plane that divides the body or organ into right and left sides.

sagittal suture – joint that unites the right and left parietal bones at the midline along the top of the skull.

saliva – aqueous solution of proteins and ions secreted into the mouth by the salivary glands.

salivary amylase – digestive enzyme in saliva that acts on starch.

salivary gland – an exocrine gland that secretes a digestive fluid called saliva.

salivation – secretion of saliva.

saltatory conduction – quick propagation of the action potential along a myelinated axon owing to voltage-gated Na⁺ channels being present only at the nodes of Ranvier.

saphenous nerve – systemic nerve of the lower anterior leg that is a branch from the femoral nerve.

sarcomere – longitudinally, repeating functional unit of skeletal muscle, with all the contractile and associated proteins involved in contraction.

sarcolemma – plasma membrane of a skeletal muscle fibres.

sarcopenia – age-related muscle atrophy.

sarcoplasm – cytoplasm of a muscle cell.

sarcoplasmic reticulum (SR) – specialised smooth endoplasmic reticulum, which stores, releases, and retrieves Ca²⁺.

satellite cell – stem cell that helps to repair muscle cells.

saturated fatty acid – long-chain hydrocarbon with single covalent bonds in the carbon chain; the number of hydrogen atoms attached to the carbon skeleton is maximised.

scala tympani – portion of the cochlea that extends from the apex to the round window.

scala vestibuli – portion of the cochlea that extends from the oval window to the apex.

scaphoid – from the lateral side, the first of the four proximal carpal bones; articulates with the radius proximally, the trapezoid, trapezium, and capitate distally, and the lunate medially.

scapula – shoulder blade bone located on the posterior side of the shoulder.

scar – collagen-rich skin formed after the process of wound healing that is different from normal skin.

Schwann cell – neuroglial cell that produces myelin in the peripheral nervous system.

sciatic nerve – systemic nerve from the sacral plexus that is a combination of the tibial and fibular nerves and extends across the hip joint and gluteal region into the upper posterior leg.

sciatica – painful condition resulting from inflammation or compression of the sciatic nerve or any of the spinal nerves that contribute to it.

sclera – white of the eye.

sclerotome – medial portion of a somite consisting of mesenchyme tissue that will give rise to bone, cartilage and fibrous connective tissues.

scoliosis – abnormal lateral curvature of the vertebral column.

scrotum – external pouch of skin and muscle that houses the testes.

sebaceous gland – type of oil gland found in the dermis all over the body and helps to lubricate and waterproof the skin and hair by secreting sebum.

sebum – oily substance that is composed of a mixture of lipids that lubricates the skin and hair.

second messenger – molecule that initiates a signalling cascade in response to hormone binding on a cell membrane receptor and activation of a G protein.

secondary adaptive response – immune response observed upon re-exposure to a pathogen, which is stronger and faster than a primary response.

secondary curve – posteriorly concave curvatures of the cervical and lumbar regions of the vertebral column that develop after the time of birth.

secondary follicles – ovarian follicles with a primary oocyte and multiple layers of granulosa cells.

secondary lymphoid organs – sites where lymphocytes mount adaptive immune responses; examples include lymph nodes and spleen.

secondary ossification centre – region of bone development in the epiphyses.

secondary sex characteristics – physical characteristics that are influenced by sex steroid hormones and have supporting roles in reproductive function.

secondary structure – regular structure that proteins form by intramolecular hydrogen bonding between the oxygen atom of one amino acid residue and the hydrogen attached to the nitrogen atom of another amino acid residue.

secondary union – wound healing facilitated by wound contraction.

secondary vesicle – five vesicles that develop from primary vesicles, continuing the process of differentiation of the embryonic brain.

secretory phase – phase of the menstrual cycle in which the endometrium secretes a nutrient-rich fluid in preparation for implantation of an embryo.

section – in anatomy, a single flat surface of a three-dimensional structure that has been cut through.

segmentation – alternating contractions and relaxations of non-adjacent segments of the intestine that move food forward and backward, breaking it apart and mixing it with digestive secretions.

selective permeability – feature of any barrier that allows certain substances to cross but excludes others.

sella turcica – elevated area of sphenoid bone located at midline of the middle cranial fossa.

semen – ejaculatory fluid composed of sperm and secretions from the seminal vesicles, prostate, and bulbourethral glands.

semicircular canals – structures within the inner ear responsible for transducing rotational movement information.

semilunar valves – valves located at the base of the pulmonary trunk and at the base of the aorta.

seminal vesicle – gland that produces seminal fluid, which contributes to semen.

seminiferous tubules – tube structures within the testes where spermatogenesis occurs.

sensation – nervous system function that receives information from the environment and translates it into the electrical signals of nervous tissue.

sensitisation – first exposure to an antigen.

sensor – (also, receptor) reports a monitored physiological value to the control centre.

sensory homunculus – topographic representation of the body within the somatosensory cortex demonstrating the correspondence between neurons processing stimuli and sensitivity.

sensory modality – a particular system for interpreting and perceiving environmental stimuli by the nervous system.

sepsis – (also, septicaemia) organismal-level inflammatory response to a massive infection.

septal cartilage – flat cartilage structure that forms the anterior portion of the nasal septum.

septic shock – (also, blood poisoning) type of shock that follows a massive infection resulting in organism-wide inflammation.

septum – (plural = septa) walls or partitions that divide the heart into chambers.

septum primum – flap of tissue in the foetus that covers the foramen ovale within a few seconds after birth.

seroconversion – clearance of pathogen in the serum and the simultaneous rise of serum antibody.

serous gland – group of cells within the serous membrane that secrete a lubricating substance onto the surface.

serous membrane – membrane that covers organs and reduces friction; also referred to as serosa.

serosa – membrane that covers organs and reduces friction; also referred to as serous membrane.

Sertoli cells – cells that support germ cells through the process of spermatogenesis; a type of sustentacular cell.

serum – blood plasma that does not contain clotting factors.

sesamoid bone – small, round bone embedded in a tendon; protects the tendon from compressive forces.

set point – ideal value for a physiological parameter; the level or small range within which a physiological parameter such as blood pressure is stable and optimally healthful, that is, within its parameters of homeostasis.

severe combined immunodeficiency disease (SCID) – genetic mutation that affects both T cell and B cell arms of the immune response.

shaft of the femur – cylindrically shaped region that forms the central portion of the femur.

shaft of the fibula – elongated, slender portion located between the expanded ends of the fibula.

shaft of the humerus – narrow, elongated, central region of the humerus.

shaft of the radius – narrow, elongated, central region of the radius.

shaft of the tibia – triangular-shaped, central portion of the tibia.

shaft of the ulna – narrow, elongated, central region of the ulna.

short bone – cube-shaped bone that is approximately equal in length, width, and thickness; provides limited motion.

shunt – circulatory shortcut that diverts the flow of blood from one region to another.

sickle cell disease – (also, sickle cell anaemia) inherited blood disorder in which haemoglobin molecules are malformed, leading to the breakdown of RBCs that take on a characteristic sickle shape.

sigmoid colon – end portion of the colon, which terminates at the rectum.

sigmoid sinuses – enlarged veins that receive blood from the transverse sinuses; flow through the jugular foramen and into the internal jugular vein.

simple columnar epithelium – tissue that consists of a single layer of column-like cells; promotes secretion and absorption in tissues and organs.

simple cuboidal epithelium – tissue that consists of a single layer of cube-shaped cells; promotes secretion and absorption in ducts and tubules.

simple squamous epithelium – tissue that consists of a single layer of flat scale-like cells; promotes diffusion and filtration across surface.

sinoatrial (SA) node – known as the pacemaker, a specialised clump of myocardial conducting cells located in the superior portion of the right atrium that has the highest inherent rate of depolarisation that then spreads throughout the heart.

sinus rhythm – normal contractile pattern of the heart.

sinus venosus – develops into the posterior portion of the right atrium, the SA node, and the coronary sinus.

sinusoid capillary – rarest type of capillary, which has extremely large intercellular gaps in the basement membrane in addition to clefts and fenestrations; found in areas such as the bone marrow and liver where passage of large molecules occurs.

sister chromatid – one of a pair of identical chromosomes, formed during DNA replication.

size exclusion – principle of selectively allowing ions through a channel on the basis of their relative size.

skeleton – bones of the body.

skeletal muscle – usually attached to bone, under voluntary control, each cell is a fibre that is multinucleated and striated.

skeletal muscle pump – effect on increasing blood pressure within veins by compression of the vessel caused by the contraction of nearby skeletal muscle.

skeletal system – organ system composed of bones and cartilage that provides for movement, support, and protection.

skull – bony structure that forms the head, face, and jaws, and protects the brain; consists of 22 bones.

slow oxidative (SO) – muscle fibre that primarily uses aerobic respiration.

small cardiac vein – parallels the right coronary artery and drains blood from the posterior surfaces of the right atrium and ventricle; drains into the great cardiac vein.

small intestine – section of the gastrointestinal tract where most digestion and absorption occurs.

small saphenous vein – located on the lateral surface of the leg; drains blood from the superficial regions of the lower leg and foot, and leads to the popliteal vein.

smooth muscle – under involuntary control, moves internal organs, cells contain a single nucleus, are spindle-shaped, and do not appear striated; each cell is a fibre.

sodium-potassium pump – (also, Na⁺/K⁺ ATP-ase) membrane-embedded protein pump that uses ATP to move Na⁺ out of a cell and K⁺ into the cell.

soft palate – posterior region of the bottom portion of the nasal cavity that consists of skeletal muscle.

soleal line – small, diagonally running ridge located on the posterior side of the proximal tibia.

solitary nucleus – medullar nucleus that receives taste information from the facial and glossopharyngeal nerves.

soma – in neurons, that portion of the cell that contains the nucleus; the cell body, as opposed to the cell processes (axons and dendrites).

somatic cell – all cells of the body excluding gamete cells.

somatic nervous system (SNS) – functional division of the nervous system that is concerned with conscious perception, voluntary movement, and skeletal muscle reflexes.

somatosensation – general senses related to the body, usually thought of as the senses of touch, which would include pain, temperature, and proprioception.

somites – blocks of paraxial mesoderm cells.

spatial summation – combination of graded potentials across the neuronal cell membrane caused by signals from separate presynaptic elements that add up to initiate an action potential.

special sense – any sensory system associated with a specific organ structure, namely smell, taste, sight, hearing, and balance.

specific gravity – weight of a liquid compared to pure water, which has a specific gravity of 1.0; any solute added to water will increase its specific gravity.

sperm – (also, spermatozoon) male gamete.

spermatic cord – bundle of nerves and blood vessels that supplies the testes; contains ductus deferens.

spermatid – immature sperm cells produced by meiosis II of secondary spermatocytes.

spermatocyte – cell that results from the division of spermatogonium and undergoes meiosis I and meiosis II to form spermatids.

spermatogenesis – formation of new sperm, occurs in the seminiferous tubules of the testes.

spermatogonia – (singular = spermatogonium) diploid precursor cells that become sperm.

spermiogenesis – transformation of spermatids to spermatozoa during spermatogenesis.

S phase – stage of the cell cycle during which DNA replication occurs.

sphenoid bone – unpaired bone that forms the central base of skull.

sphenoid sinus – air-filled space located within the sphenoid bone; most posterior of the paranasal sinuses.

sphygmomanometer – blood pressure cuff attached to a device that measures blood pressure.

spinal accessory nerve – eleventh cranial nerve; responsible for contraction of neck muscles.

spinal cavity – division of the dorsal cavity that houses the spinal cord; also referred to as vertebral cavity.

spinal cord – organ of the central nervous system found within the vertebral cavity and connected with the periphery through spinal nerves; mediates reflex behaviours.

spinal nerve -one of 31 nerves connected to the spinal cord.

spinal trigeminal nucleus – component of the trigeminal nuclei that is found in the medulla.

spine of the scapula – prominent ridge passing mediolaterally across the upper portion of the posterior scapular surface.

spinothalamic tract – ascending tract of the spinal cord associated with pain and temperature sensations.

spinous process – unpaired bony process that extends posteriorly from the vertebral arch of a vertebra.

spiral ganglion – location of neuronal cell bodies that transmit auditory information along the eighth cranial nerve.

spleen – secondary lymphoid organ that filters pathogens from the blood (white pulp) and removes degenerating or damaged blood cells (red pulp).

splenic artery – branch of the celiac trunk; supplies blood to the spleen.

spliceosome – complex of enzymes that serves to splice out the introns of a pre-mRNA transcript.

splicing – the process of modifying a pre-mRNA transcript by removing certain, typically non-coding, regions.

spongy bone – (also, cancellous bone) trabeculated osseous tissue that supports shifts in weight distribution.

spontaneous depolarisation – (also, prepotential depolarisation) the mechanism that accounts for the autorhythmic property of cardiac muscle; the membrane potential increases as sodium ions diffuse through the always-open sodium ion channels and causes the electrical potential to rise.

squamous cell carcinoma – type of skin cancer that originates from the stratum spinosum of the epidermis.

squamous suture – joint that unites the parietal bone to the squamous portion of the temporal bone on the lateral side of the skull.

stage of exhaustion – stage three of the general adaptation syndrome; the body’s long-term response to stress mediated by the hormones of the adrenal cortex.

stage of resistance – stage two of the general adaptation syndrome; the body’s continued response to stress after stage one diminishes.

stapes – (also, stirrup) ossicle of the middle ear that is attached to the inner ear.

starch – storage carbohydrate in plants.

stem cell – cell that is oligo-, multi-, or pluripotency that has the ability to produce additional stem cells rather than becoming further specialised.

stereocilia – array of apical membrane extensions in a hair cell that transduce movements when they are bent.

sternal angle – junction line between manubrium and body of the sternum and the site for attachment of the second rib to the sternum.

sternal end of the clavicle – medial end of the clavicle that articulates with the manubrium of the sternum.

sternoclavicular joint – articulation between the manubrium of the sternum and the sternal end of the clavicle; forms the only bony attachment between the pectoral girdle of the upper limb and the axial skeleton.

sternum – flattened bone located at the centre of the anterior chest.

steroid – type of lipid comprised of four fused hydrocarbon rings forming a planar structure.

stimulus – an event in the external or internal environment that registers as activity in a sensory neuron.

stomach – gastrointestinal tract organ that contributes to chemical and mechanical digestion of food from the oesophagus before releasing it, as chyme, to the small intestine.

straight sinus – enlarged vein that drains blood from the brain; receives most of the blood from the great cerebral vein and flows into the left or right transverse sinus.

stratified columnar epithelium – tissue that consists of two or more layers of column-like cells, contains glands and is found in some ducts.

stratified cuboidal epithelium – tissue that consists of two or more layers of cube-shaped cells, found in some ducts.

stratified squamous epithelium – tissue that consists of multiple layers of cells with the most apical being flat scale-like cells; protects surfaces from abrasion.

stratum basale – deepest layer of the epidermis, made of epidermal stem cells.

stratum corneum – most superficial layer of the epidermis.

stratum granulosum – layer of the epidermis superficial to the stratum spinosum.

stratum lucidum – layer of the epidermis between the stratum granulosum and stratum corneum, found only in thick skin covering the palms, soles of the feet, and digits.

stratum spinosum – layer of the epidermis superficial to the stratum basale, characterised by the presence of desmosomes.

stress-relaxation response – relaxation of smooth muscle tissue after being stretched.

stretch mark – mark formed on the skin due to a sudden growth spurt and expansion of the dermis beyond its elastic limits.

stretch reflex – response to activation of the muscle spindle stretch receptor that causes contraction of the muscle to maintain a constant length.

striation – alignment of parallel actin and myosin filaments which form a banded pattern.

striatum – the caudate and putamen collectively, as part of the basal nuclei, which receive input from the cerebral cortex.

stroke volume (SV) – amount of blood pumped by each ventricle per contraction; also, the difference between EDV and ESV.

styloid process – downward projecting, elongated bony process located on the inferior aspect of the skull.

styloid process of the radius – pointed projection located on the lateral end of the distal radius.

styloid process of the ulna – short, bony projection located on the medial end of the distal ulna.

stylomastoid foramen – opening located on inferior skull, between the styloid process and mastoid process.

subacromial bursa – bursa that protects the supraspinatus muscle tendon and superior end of the humerus from rubbing against the acromion of the scapula.

subarachnoid space – space between the arachnoid mater and pia mater that contains CSF and the fibrous connections of the arachnoid trabeculae.

subclavian artery – right subclavian arises from the brachiocephalic artery, whereas the left subclavian artery arises from the aortic arch; gives rise to the internal thoracic, vertebral, and thyrocervical arteries; supplies blood to the arms, chest, shoulders, back, and central nervous system.

subclavian vein – located deep in the thoracic cavity; becomes the axillary vein as it enters the axillary region; drains the axillary and smaller local veins near the scapular region; leads to the brachiocephalic vein.

subcortical nucleus – all the nuclei beneath the cerebral cortex, including the basal nuclei and the basal forebrain.

subcutaneous bursa – bursa that prevents friction between skin and an underlying bone.

sublingual gland – one of a pair of major salivary glands located beneath the tongue.

submandibular gland – one of a pair of major salivary glands located in the floor of the mouth.

submodality – specific sense within a broader major sense such as sweet as a part of the sense of taste, or colour as a part of vision.

submucosa – layer of dense connective tissue in the gastrointestinal tract wall that binds the overlying mucosa to the underlying muscularis.

submuscular bursa – bursa that prevents friction between bone and a muscle or between adjacent muscles.

submucosal plexus – (plexus of Meissner) nerve supply that regulates activity of glands and smooth muscle.

subpubic angle – inverted V-shape formed by the convergence of the right and left ischiopubic rami; this angle is greater than 80 degrees in females and less than 70 degrees in males.

subscapular bursa – bursa that prevents rubbing of the subscapularis muscle tendon against the scapula.

subscapular fossa – broad depression located on the anterior (deep) surface of the scapula.

subscapular vein – drains blood from the subscapular region and leads to the axillary vein.

subtalar joint – articulation between the talus and calcaneus bones of the foot; allows motions that contribute to inversion/eversion of the foot.

substantia nigra pars compacta – nuclei within the basal nuclei that release dopamine to modulate the function of the striatum; part of the motor pathway.

substantia nigra pars reticulata – nuclei within the basal nuclei that serve as an output centre of the nuclei; part of the motor pathway.

subtendinous bursa – bursa that prevents friction between bone and a muscle tendon.

subthalamus – nucleus within the basal nuclei that is part of the indirect pathway.

sucrase – brush border enzyme that breaks down sucrose into glucose and fructose.

sudoriferous gland – sweat gland.

sulcus – (plural = sulci) fat-filled groove visible on the surface of the heart; coronary vessels are also located in these areas.

summate – to add together, as in the cumulative change in postsynaptic potentials toward reaching threshold in the membrane, either across a span of the membrane or over a certain amount of time.

superficial – describes a position nearer to the surface of the body.

superficial burns – superficial burn that injures only the epidermis.

superior – describes a position above or higher than another part of the body proper; also referred to as cranial.

superior angle of the scapula – corner of the scapula between the superior and medial borders of the scapula.

superior articular process – bony process that extends upward from the vertebral arch of a vertebra that articulates with the inferior articular process of the next higher vertebra.

superior articular process of the sacrum – paired processes that extend upward from the sacrum to articulate (join) with the inferior articular processes from the L5 vertebra.

superior border of the scapula – superior margin of the scapula.

superior colliculus – half of the midbrain tectum that is responsible for aligning visual, auditory, and somatosensory spatial perceptions.

superior oblique – extraocular muscle responsible for medial rotation of the eye.

superior pubic ramus – narrow segment of bone that passes laterally from the pubic body to join the ilium.

superior rectus – extraocular muscle responsible for looking up.

superior rotation – movement of the scapula during upper limb abduction in which the glenoid cavity of the scapula moves in an upward direction as the medial end of the scapular spine moves in a downward direction.

superior sagittal sinus – dural sinus that runs along the top of the longitudinal fissure and drains blood from the majority of the outer cerebrum.

supplemental motor area – cortical area anterior to the primary motor cortex that is responsible for planning movements.

suprachiasmatic nucleus – hypothalamic target of the retina that helps to establish the circadian rhythm of the body based on the presence or absence of daylight.

supraglenoid tubercle – small bump located at the superior margin of the glenoid cavity.

suprascapular notch – small notch located along the superior border of the scapula, medial to the coracoid process.

supraspinous fossa – narrow depression located on the posterior scapula, superior to the spine.

supraspinous ligament – ligament that interconnects the spinous processes of the thoracic and lumbar vertebrae.

superior mesenteric artery – branch of the abdominal aorta; supplies blood to the small intestine (duodenum, jejunum, and ileum), the pancreas, and a majority of the large intestine.

superior nasal concha – smallest and most superiorly located of the nasal conchae; formed by the ethmoid bone.

superior nuchal line – paired bony lines on the posterior skull that extend laterally from the external occipital protuberance.

superior orbital fissure – irregularly shaped opening between the middle cranial fossa and the posterior orbit.

superior phrenic artery – branch of the thoracic aorta; supplies blood to the superior surface of the diaphragm.

superior sagittal sinus – enlarged vein located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri; receives most of the blood drained from the superior surface of the cerebrum and leads to the inferior jugular vein and the vertebral vein.

superior vena cava – large systemic vein that returns blood to the heart from the superior portion of the body.

supine – face up.

supinated position – forearm position in which the palm faces anteriorly (anatomical position).

supination – forearm motion that moves the palm of the hand from the palm backward to the palm forward position.

supportive connective tissue – type of connective tissue that provides strength to the body and protects soft tissue.

supraorbital foramen – opening located on anterior skull, at the superior margin of the orbit.

supraorbital margin – superior margin of the orbit.

surgical neck – region of the humerus where the expanded, proximal end joins with the narrower shaft.

suspensory ligaments – bands of connective tissue that suspend the breast onto the chest wall by attachment to the overlying dermis.

sustentaculum tali – bony ledge extending from the medial side of the calcaneus bone.

suture – junction line at which adjacent bones of the skull are united by fibrous connective tissue.

sympathetic chain ganglia – autonomic ganglia in a chain along the anterolateral aspect of the vertebral column that are responsible for contributing to homeostatic mechanisms of the autonomic nervous system.

symphysis – type of cartilaginous joint where the bones are joined by fibrocartilage.

synapse – narrow junction across which a chemical signal passes from neuron to the next, initiating a new electrical signal in the target cell.

synaptic cleft – space between a nerve (axon) terminal and a motor end-plate.

synaptic end bulb – swelling at the end of an axon where neurotransmitter molecules are released onto a target cell across a synapse.

synarthrosis – immobile or nearly immobile joint.

synchondrosis – type of cartilaginous joint where the bones are joined by hyaline cartilage.

syncytiotrophoblast – superficial cells of the trophoblast that fuse to form a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall.

syndesmosis – type of fibrous joint in which two separated, parallel bones are connected by an interosseous membrane.

synaptic cleft – small gap between cells in a chemical synapse where neurotransmitter diffuses from the presynaptic element to the postsynaptic element.

synostosis – site at which adjacent bones or bony components have fused together.

synovial fluid – thick, lubricating fluid that fills the interior of a synovial joint.

synovial joint – joint at which the articulating surfaces of the bones are located within a joint cavity formed by an articular capsule.

synovial membrane – connective tissue membrane that lines the cavities of freely movable joints, producing synovial fluid for lubrication.

systemic anatomy – study of the structures that contribute to specific body systems.

systemic circuit – blood flow to and from virtually all of the tissues of the body.

systemic nerve – nerve in the periphery distal to a nerve plexus or spinal nerve.

systemic oedema – increased fluid retention in the interstitial spaces and cells of the body; can be seen as swelling over large areas of the body, particularly the lower extremities.

systole – period of time when the heart muscle is contracting.

systolic pressure – larger number recorded when measuring arterial blood pressure; represents the maximum value following ventricular contraction.

T

talocrural joint – ankle joint; articulation between the talus bone of the foot and medial malleolus of the tibia, distal tibia, and lateral malleolus of the fibula; a uniaxial hinge joint that allows only for dorsiflexion and plantar flexion of the foot.

talus – tarsal bone that articulates superiorly with the tibia and fibula at the ankle joint; also articulates inferiorly with the calcaneus bone and anteriorly with the navicular bone.

target heart rate – range in which both the heart and lungs receive the maximum benefit from an aerobic workout.

tarsal bone – one of the seven bones that make up the posterior foot; includes the calcaneus, talus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and lateral cuneiform bones.

taste buds – structures within a papilla on the tongue that contain gustatory receptor cells.

T cell – lymphocyte that acts by secreting molecules that regulate the immune system or by causing the destruction of foreign cells, viruses, and cancer cells.

T cell-dependent antigen – antigen that binds to B cells, which requires signals from T cells to make antibody.

T cell-independent antigen – binds to B cells, which do not require signals from T cells to make antibody.

T cell tolerance – process during T cell differentiation where most T cells that recognise antigens from one’s own body are destroyed.

tectorial membrane – component of the organ of Corti that lays over the hair cells, into which the stereocilia are embedded.

tectospinal tract – extrapyramidal connections between the superior colliculus and spinal cord.

tectum – region of the midbrain, thought of as the roof of the cerebral aqueduct, which is subdivided into the inferior and superior colliculi.

tegmentum – region of the midbrain, thought of as the floor of the cerebral aqueduct, which continues into the pons and medulla as the floor of the fourth ventricle.

telencephalon – secondary vesicle of the embryonic brain that develops into the cerebrum.

telogen – resting phase of the hair growth cycle initiated with catagen and terminated by the beginning of a new anagen phase of hair growth.

telophase – final stage of mitosis (and meiosis), preceding cytokinesis, characterised by the formation of two new daughter nuclei.

temporal bone – paired bones that form the lateral, inferior portions of the skull, with squamous, mastoid, and petrous portions.

temporal fossa – shallow space on the lateral side of the skull, above the level of the zygomatic arch.

temporal lobe – region of the cerebral cortex directly beneath the temporal bone of the cranium.

temporal process of the zygomatic bone – short extension from the zygomatic bone that forms the anterior portion of the zygomatic arch.

temporal summation – combination of graded potentials at the same location on a neuron resulting in a strong signal from one input.

temporal vein – drains blood from the temporal region and leads to the external jugular vein.

temporomandibular joint (TMJ) – articulation between the condyle of the mandible and the mandibular fossa and articular tubercle of the temporal bone of the skull; allows for depression/elevation (opening/closing of mouth), protraction/retraction, and side-to-side motions of the mandible.

tendon – dense connective tissue structure that anchors a muscle to bone.

tendon sheath – connective tissue that surrounds a tendon at places where the tendon crosses a joint; contains a lubricating fluid to prevent friction and allow smooth movements of the tendon.

teniae coli – one of three smooth muscle bands that make up the longitudinal muscle layer of the muscularis in all the large intestine except the terminal end.

terminal ganglion – autonomic ganglia that are near or within the walls of organs that are responsible for contributing to homeostatic mechanisms of the autonomic nervous system.

tertiary follicles – (also, antral follicles) ovarian follicles with a primary or secondary oocyte, multiple layers of granulosa cells, and a fully formed antrum.

tertiary structure – a protein’s three-dimensional conformation, including interactions between secondary structural elements; formed from interactions between amino acid side chains.

testes – (singular = testis) male gonads.

testicular artery – branch of the abdominal aorta; will ultimately travel outside the body cavity to the testes and form one component of the spermatic cord.

testicular vein – drains the testes and forms part of the spermatic cord; the right testicular vein empties directly into the inferior vena cava and the left testicular vein empties into the left renal vein.

testosterone – steroid hormone secreted by the male testes and important in the maturation of sperm cells, growth and development of the male reproductive system, and the development of male secondary sex characteristics.

tetanus – a continuous fused contraction.

thalamus – region of the central nervous system that acts as a relay for sensory pathways.

thalassaemia – inherited blood disorder in which the life-span of RBCs is significantly reduced due to unbalanced production of globin chains.

theca cells – androgen-producing cells in a maturing ovarian follicle.

thermoreceptor – type of sensory receptor capable of transducing temperature stimuli into neural action potentials.

thick filament – the thick myosin strands and their multiple heads projecting from the centre of the sarcomere toward, but not all to way to, the Z-discs.

thigh – portion of the lower limb located between the hip and knee joints.

thin filament – thin strands of actin and its troponin-tropomyosin complex projecting from the Z-discs toward the centre of the sarcomere.

third ventricle – portion of the ventricular system that is in the region of the diencephalon.

thoracic aorta – portion of the descending aorta superior to the aortic hiatus.

thoracic cage – consists of 12 pairs of ribs and sternum.

thoracic cavity – division of the anterior (ventral) cavity that houses the heart, lungs, oesophagus, and trachea.

thoracic curve – anteriorly concave curvature of the thoracic vertebral column region; a primary curve of the vertebral column.

thoracic duct – large duct that drains lymph from the lower limbs, left thorax, left upper limb, and the left side of the head.

thoracic wall compliance – ability of the thoracic wall to stretch while under pressure.

thoracic vertebrae – twelve vertebrae numbered as T1–T12 that are located in the thoracic region (upper back) of the vertebral column.

thoroughfare channel – continuation of the metarteriole that enables blood to bypass a capillary bed and flow directly into a venule, creating a vascular shunt.

threshold – membrane voltage at which an action potential is initiated.

thrombin – enzyme essential for conversion of soluble plasma fibrinogen to insoluble fibrin.

thrombosis – excessive clot formation.

thrombus – aggregation of fibrin, platelets, and erythrocytes in an intact artery or vein.

thrombocytes – platelets, one of the formed elements of blood that consists of cell fragments broken off from megakaryocytes.

thrombocytopenia – condition in which there are too few platelets, resulting in abnormal bleeding (haemophilia).

thrombocytosis – condition in which there are too many platelets, resulting in abnormal clotting (thrombosis).

thrombopoietin – hormone secreted by the liver and kidneys that prompts the development of

thymocyte – immature T cell found in the thymus.

thymosins – hormones produced and secreted by the thymus that play an important role in the development and differentiation of T cells.

thymus – primary lymphoid organ; where T lymphocytes proliferate and mature megakaryocytes into thrombocytes (platelets).

thyrocervical artery – arises from the subclavian artery; supplies blood to the thyroid, the cervical region, the upper back, and shoulder.

thyroid cartilage – largest piece of cartilage that makes up the larynx and consists of two lamina.

thyroid gland – large endocrine gland responsible for the synthesis of thyroid hormones.

thyroid-stimulating hormone (TSH) – anterior pituitary hormone that triggers secretion of thyroid hormones by the thyroid gland (also called thyrotropin).

thyroxine – (also, tetraiodothyronine, T4) amino acid–derived thyroid hormone that is more abundant but less potent than T3 and often converted to T3 by target cells.

Th1 cells – cells that secrete cytokines that enhance the activity of macrophages and other cells.

Th2 cells – cells that secrete cytokines that induce B cells to differentiate into antibody-secreting plasma cells.

tibia – shin bone; the large, weight-bearing bone located on the medial side of the leg.

tibial collateral ligament – extrinsic ligament of knee joint that spans from the medial epicondyle of the femur to the medial tibia; resists hyperextension and rotation of extended knee.

tibial nerve – systemic nerve of the posterior leg that begins as part of the sciatic nerve.

tibial tuberosity – elevated area on the anterior surface of the proximal tibia.

tidal volume (TV) – amount of air that normally enters the lungs during quiet breathing.

tight junction – forms an impermeable barrier between cells.

tissue – group of similar or closely related cells that act together to perform a specific function.

tissue factor – protein thromboplastin, which initiates the extrinsic pathway when exposed to clotting factor VII as a result of tissue damage.

tissue membrane – thin layer or sheet of cells that covers the outside of the body, organs, and internal cavities.

tissue typing – typing of MHC molecules between a recipient and donor for use in a potential transplantation procedure.

T lymphocytes – (also, T cells) lymphocytes that provide cellular-level immunity by physically attacking foreign or diseased cells.

tongue – accessory digestive organ of the mouth, the bulk of which is composed of skeletal muscle.

tonsils – lymphoid nodules associated with the nasopharynx.

topographical – relating to positional information.

total dead space – sum of the anatomical dead space and alveolar dead space.

total lung capacity (TLC) – total amount of air that can be held in the lungs; sum of TV, ERV, IRV, and RV.

total pressure – sum of all the partial pressures of a gaseous mixture.

totipotent – embryonic cells that have the ability to differentiate into any type of cell and organ in the body.

totipotent stem cell – embryonic stem cell that is capable of differentiating into any and all cells of the body, enabling the full development of an organism.

trabeculae – (singular = trabecula) spikes or sections of the lattice-like matrix in spongy bone.

trabeculae carneae – ridges of muscle covered by endocardium located in the ventricles.

trachea – tube composed of cartilaginous rings and supporting tissue that connects the lung bronchi and the larynx; provides a route for air to enter and exit the lung.

trachealis muscle – smooth muscle located in the fibroelastic membrane of the trachea.

tract – bundle of axons in the central nervous system having the same function and point of origin.

transcription – process of producing an mRNA molecule that is complementary to a particular gene of DNA.

transcription factor – one of the proteins that regulate the transcription of genes.

transduction – process of changing an environmental stimulus into the electrochemical signals of the nervous system.

trans fat – fat formed artificially by hydrogenating oils, leading to a different arrangement of double bond(s) than those in naturally occurring lipids.

transferrin – plasma protein that binds reversibly to iron and distributes it throughout the body.

transient ischemic attack (TIA) – temporary loss of neurological function caused by a brief interruption in blood flow; also known as a mini-stroke.

transitional epithelium – form of stratified epithelium found in the urinary tract, characterised by an apical layer of cells that change shape in response to the presence of urine.

transfer RNA (tRNA) – molecules of RNA that serve to bring amino acids to a growing polypeptide strand and properly place them into the sequence.

translation – process of producing a protein from the nucleotide sequence code of an mRNA transcript.

transpulmonary pressure – pressure difference between the intrapleural and intra-alveolar pressures.

transverse colon – part of the colon between the ascending colon and the descending colon.

transverse foramen – opening found only in the transverse processes of cervical vertebrae.

transverse plane – two-dimensional, horizontal plane that divides the body or organ into superior and inferior portions.

transverse process – paired bony processes that extends laterally from the vertebral arch of a vertebra.

transverse sinuses – pair of enlarged veins near the lambdoid suture that drain the occipital, sagittal, and straight sinuses, and leads to the sigmoid sinuses.

trapezium – from the lateral side, the first of the four distal carpal bones; articulates with the scaphoid proximally, the first and second metacarpals distally, and the trapezoid medially.

trapezoid – from the lateral side, the second of the four distal carpal bones; articulates with the scaphoid proximally, the second metacarpal distally, the trapezium laterally, and the capitate medially.

treppe – stepwise increase in contraction tension.

triacylglycerol (also, triglyceride) – fat molecule; consists of three fatty acids linked to a glycerol molecule.

triad – the grouping of one T-tubule and two terminal cisternae.

tricuspid valve – term used most often in clinical settings for the right atrioventricular valve.

trigeminal ganglion – sensory ganglion that contributes sensory fibres to the trigeminal nerve.

trigeminal nerve – fifth cranial nerve; responsible for cutaneous sensation of the face and contraction of the muscles of mastication.

trigone – area at the base of the bladder marked by the two ureters in the posterior–lateral aspect and the urethral orifice in the anterior aspect oriented like points on a triangle.

triiodothyronine – (also, T3) amino acid–derived thyroid hormone that is less abundant but more potent than T4.

triplet – consecutive sequence of three nucleotides on a DNA molecule that, when transcribed into an mRNA codon, corresponds to a particular amino acid.

triquetrum – from the lateral side, the third of the four proximal carpal bones; articulates with the lunate laterally, the hamate distally, and has a facet for the pisiform.

trochlea – pulley-shaped region located medially at the distal end of the humerus; articulates at the elbow with the trochlear notch of the ulna.

trochlear nerve – fourth cranial nerve; responsible for contraction of one of the extraocular muscles.

trochlear notch – large, C-shaped depression located on the anterior side of the proximal ulna; articulates at the elbow with the trochlea of the humerus.

trophoblast – fluid-filled shell of squamous cells destined to become the chorionic villi, placenta, and associated foetal membranes.

troponin – regulatory protein that binds to actin, tropomyosin, and calcium.

tropomyosin – regulatory protein that covers myosin-binding sites to prevent actin from binding to myosin.

true ribs – vertebrosternal ribs 1–7 that attach via their costal cartilage directly to the sternum.

true vocal cord – one of the pair of folded, white membranes that have a free inner edge that oscillates as air passes through to produce sound.

truncus arteriosus – portion of the primitive heart that will eventually divide and give rise to the ascending aorta and pulmonary trunk.

tubercle of the rib – small bump on the posterior side of a rib for articulation with the transverse process of a thoracic vertebra.

T-tubule – projection of the sarcolemma into the interior of the cell.

trunk – large vessel that gives rise to smaller vessels.

tubuloglomerular feedback – feedback mechanism involving the JGA; macula densa cells monitor Na⁺ concentration in the terminal portion of the ascending loop of Henle and act to cause vasoconstriction or vasodilation of afferent and efferent arterioles to alter GFR.

tunica externa – (also, tunica adventitia) outermost layer or tunic of a vessel (except capillaries).

tunica intima – (also, tunica interna) innermost lining or tunic of a vessel.

tunica media – middle layer or tunic of a vessel (except capillaries).

T wave – component of the electrocardiogram that represents the repolarisation of the ventricles.

twitch – single contraction produced by one action potential.

tympanic membrane – ear drum.

type I alveolar cell – squamous epithelial cells that are the major cell type in the alveolar wall; highly permeable to gases.

type II alveolar cell – cuboidal epithelial cells that are the minor cell type in the alveolar wall; secrete pulmonary surfactant.

type I hypersensitivity – immediate response mediated by mast cell degranulation caused by the crosslinking of the antigen-specific IgE molecules on the mast cell surface.

type II hypersensitivity – cell damage caused by the binding of antibody and the activation of complement, usually against red blood cells.

type III hypersensitivity – damage to tissues caused by the deposition of antibody-antigen (immune) complexes followed by the activation of complement.

U

ulna – bone located on the medial side of the forearm.

ulnar artery – formed at the bifurcation of the brachial artery; parallels the ulna; gives off smaller branches until it reaches the carpal region where it fuses with the radial artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region.

ulnar collateral ligament – intrinsic ligament on the medial side of the elbow joint; spans from the medial epicondyle of the humerus to the medial ulna.

ulnar nerve – systemic nerve of the arm located close to the ulna, a bone of the forearm.

ulnar notch of the radius – shallow, smooth area located on the medial side of the distal radius; articulates with the head of the ulna at the distal radioulnar joint.

ulnar tuberosity – roughened area located on the anterior, proximal ulna inferior to the coronoid process.

ulnar vein – parallels the ulna and ulnar artery; arises from the palmar venous arches and leads to the brachial vein.

umami – taste submodality for sensitivity to the concentration of amino acids; also called the savory sense.

umbilical arteries – pair of vessels that runs within the umbilical cord and carries foetal blood low in oxygen and high in waste to the placenta for exchange with maternal blood.

umbilical cord – connection between the developing conceptus and the placenta; carries deoxygenated blood and wastes from the foetus and returns nutrients and oxygen from the mother.

umbilical vein – single vessel that originates in the placenta and runs within the umbilical cord, carrying oxygen- and nutrient-rich blood to the foetal heart.

uniaxial joint – type of diarthrosis; joint that allows for motion within only one plane (one axis).

unipolar – shape of a neuron which has only one process that includes both the axon and dendrite.

unipotent – describes the condition of being committed to a single specialised cell type.

universal RBC donor – individual with type O− blood.

universal RBC recipient – individual with type AB+ blood.

unsaturated fatty acid – long-chain hydrocarbon that has one or more double bonds in the hydrocarbon chain.

upper motor neuron – first neuron in the motor command pathway with its cell body in the cerebral cortex that synapses on the lower motor neuron in the spinal cord.

upper oesophageal sphincter – skeletal muscle sphincter that regulates food movement from the pharynx to the oesophagus.

upregulation – increase in the number of hormone receptors, typically in response to chronically reduced levels of a hormone.

urethra – transports urine from the bladder to the outside environment.

urinalysis – analysis of urine to diagnose disease.

urochrome – haem-derived pigment that imparts the typical yellow colour of urine.

uterine tubes – (also, fallopian tubes or oviducts) ducts that facilitate transport of an ovulated oocyte to the uterus.

uterus – muscular hollow organ in which a fertilised egg develops into a foetus.

utricle – structure of the inner ear responsible for transducing linear acceleration in the horizontal plane.

V

vagina – tunnel-like organ that provides access to the uterus for the insertion of semen and from the uterus for the birth of a baby.

vagus nerve – tenth cranial nerve; responsible for the autonomic control of organs in the thoracic and upper abdominal cavities.

Valsalva’s manoeuvre – voluntary contraction of the diaphragm and abdominal wall muscles and closing of the glottis, which increases intra-abdominal pressure and facilitates defecation.

valve – in the cardiovascular system, a specialised structure located within the heart or vessels that ensures one-way flow of blood.

variable region domain – part of a lymphocyte antigen receptor that varies considerably between different receptor types.

varicosity – enlargement of neurons that release neurotransmitters into synaptic clefts.

vasa recta – branches of the efferent arterioles that parallel the course of the loops of Henle and are continuous with the peritubular capillaries; with the glomerulus, form a portal system.

vasa vasorum – small blood vessels located within the walls or tunics of larger vessels that supply nourishment to and remove wastes from the cells of the vessels.

vasodilation – widening of blood vessels.

vascular shock – type of shock that occurs when arterioles lose their normal muscular tone and dilate dramatically.

vascular shunt – continuation of the metarteriole and thoroughfare channel that allows blood to bypass the capillary beds to flow directly from the arterial to the venous circulation.

vascular spasm – initial step in haemostasis, in which the smooth muscle in the walls of the ruptured or damaged blood vessel contracts.

vascular tone – contractile state of smooth muscle in a blood vessel.

vascular tubes – rudimentary blood vessels in a developing foetus.

vascular tunic – middle layer of the eye primarily composed of connective tissue with a rich blood supply.

vasoconstriction – constriction of the smooth muscle of a blood vessel, resulting in a decreased vascular diameter.

vasodilation – relaxation of the smooth muscle in the wall of a blood vessel, resulting in an increased vascular diameter.

vasomotion – irregular, pulsating flow of blood through capillaries and related structures.

vein – blood vessel that conducts blood toward the heart.

venous reserve – volume of blood contained within systemic veins in the integument, bone marrow, and liver that can be returned to the heart for circulation, if needed.

ventilation – movement of air into and out of the lungs; consists of inspiration and expiration.

ventral – describes the front or direction toward the front of the body; also referred to as anterior.

ventral cavity – larger body cavity located anterior to the posterior (dorsal) body cavity; includes the serous membrane-lined pleural cavities for the lungs, pericardial cavity for the heart, and peritoneal cavity for the abdominal and pelvic organs; also referred to as anterior body cavity.

ventral (anterior) nerve root – axons emerging from the anterior or lateral horns of the spinal cord.

ventral posterior nucleus – nucleus in the thalamus that is the target of gustatory sensations and projects to the cerebral cortex.

ventral respiratory group (VRG) – region of the medulla oblongata that stimulates the contraction of the accessory muscles involved in respiration to induce forced inspiration and expiration.

ventral stream – connections between cortical areas from the occipital lobe to the temporal lobe that are responsible for identification of visual stimuli.

ventricle – one of the primary pumping chambers of the heart located in the lower portion of the heart; the left ventricle is the major pumping chamber on the lower left side of the heart that ejects.

ventricle – central cavity within the brain where CSF is produced and circulates.

ventricular ejection phase – second phase of ventricular systole during which blood is pumped from the ventricle.

venule – small vessel leading from the capillaries to veins.

vernix caseosa – waxy, cheese-like substance that protects the delicate foetal skin until birth.

vertebra – individual bone in the neck and back regions of the vertebral column.

vertebral arch – bony arch formed by the posterior portion of each vertebra that surrounds and protects the spinal cord.

vertebral artery – arises from the subclavian artery and passes through the vertebral foramen through the foramen magnum to the brain; joins with the internal carotid artery to form the arterial circle; supplies blood to the brain and spinal cord.

vertebral column – entire sequence of bones that extend from the skull to the tailbone.

vertebral (spinal) canal – bony passageway within the vertebral column for the spinal cord that is formed by the series of individual vertebral foramina.

vertebral foramen – opening associated with each vertebra defined by the vertebral arch that provides passage for the spinal cord.

vertebral vein – arises from the base of the brain and the cervical region of the spinal cord; passes through the intervertebral foramina in the cervical vertebrae; drains smaller veins from the cranium, spinal cord, and vertebrae, and leads to the brachiocephalic vein; counterpart of the vertebral artery.

vesicle – membrane-bound structure that contains materials within or outside of the cell.

vestibular ganglion – location of neuronal cell bodies that transmit equilibrium information along the eighth cranial nerve.

vestibular fold – part of the folded region of the glottis composed of mucous membrane; supports the epiglottis during swallowing.

vestibular nuclei – targets of the vestibular component of the eighth cranial nerve.

vestibule – in the ear, the portion of the inner ear responsible for the sense of equilibrium.

vestibulocochlear nerve – eighth cranial nerve; responsible for the sensations of hearing and balance.

vestibulo-ocular reflex (VOR) – reflex based on connections between the vestibular system and the cranial nerves of eye movements that ensures images are stabilised on the retina as the head and body move.

vestibulospinal tract – extrapyramidal connections between the vestibular nuclei in the brain stem and spinal cord that modulate movement and contribute to balance based on the sense of equilibrium.

villus – projection of the mucosa of the small intestine.

visceral branches – branches of the descending aorta that supply blood to the viscera.

visceral muscle – smooth muscle found in the walls of visceral organs.

visceral pleura – innermost layer of the pleura that is superficial to the lungs and extends into the lung fissures.

visceral sense – sense associated with the internal organs.

vision – special sense of sight based on transduction of light stimuli.

visual acuity – property of vision related to the sharpness of focus, which varies in relation to retinal position.

vital capacity (VC) – sum of TV, ERV, and IRV, which is all the volumes that participate in gas exchange.

vitamin D – compound that aids absorption of calcium and phosphates in the intestine to improve bone health.

vitiligo – skin condition in which melanocytes in certain areas lose the ability to produce melanin, possibly due an autoimmune reaction that leads to loss of colour in patches.

vitreous humour – viscous fluid that fills the posterior chamber of the eye.

voltage-gated channel – ion channel that opens because of a change in the charge distributed across the membrane where it is located.

voltage-gated sodium channels – membrane proteins that open sodium channels in response to a sufficient voltage change, and initiate and transmit the action potential as Na⁺ enters through the channel.

voluntary phase – initial phase of deglutition, in which the bolus moves from the mouth to the oropharynx.

vomer bone – unpaired bone that forms the inferior and posterior portions of the nasal septum.

vulva – external female genitalia.

W

wax – lipid comprised of a long-chain fatty acid that is esterified to a long-chain alcohol; serves as a protective coating on some feathers, aquatic mammal fur, and leaves.

wave summation – addition of successive neural stimuli to produce greater contraction.

white blood cells (WBCs) – (also, leukocytes) one of the formed elements of blood that provides defence against disease agents and foreign materials.

white matter – regions of the nervous system containing mostly myelinated axons, making the tissue appear white because of the high lipid content of myelin.

Wolffian duct – duct system present in the embryo that will eventually form the internal male reproductive structures.

working memory – function of the prefrontal cortex to maintain a representation of information that is not in the immediate environment.

wound contraction – process whereby the borders of a wound are physically drawn together.

X

xiphoid process – small process that forms the inferior tip of the sternum.

Y

yellow marrow – connective tissue in the interior cavity of a bone where fat is stored.

yolk sac – membrane associated with primitive circulation to the developing embryo; source of the first blood cells and germ cells and contributes to the umbilical cord structure.

Z

zona fasciculata – intermediate region of the adrenal cortex that produce hormones called glucocorticoids.

zona glomerulosa – most superficial region of the adrenal cortex, which produces the hormones collectively referred to as mineralocorticoids.

zona pellucida – thick, gel-like glycoprotein membrane that coats the oocyte and must be penetrated by sperm before fertilisation can occur.

zona reticularis – deepest region of the adrenal cortex, which produces the steroid sex hormones called androgens.

zone of calcified matrix – region of the epiphyseal plate closest to the diaphyseal end; functions to connect the epiphyseal plate to the diaphysis.

zone of maturation and hypertrophy – region of the epiphyseal plate where chondrocytes from the proliferative zone grow and mature and contribute to the longitudinal growth of the epiphyseal plate.

zonule fibres – fibrous connections between the ciliary body and the lens.

zygapophysial joints – facet joints; plane joints between the superior and inferior articular processes of adjacent vertebrae that provide for only limited motions between the vertebrae.

zygomatic arch – elongated, free-standing arch on the lateral skull, formed anteriorly by the temporal process of the zygomatic bone and posteriorly by the zygomatic process of the temporal bone.

zygomatic bone – cheekbone; paired bones that contribute to the lateral orbit and anterior zygomatic arch.

zygomatic process of the temporal bone – extension from the temporal bone that forms the posterior portion of the zygomatic arch.

zygote – fertilised egg; a diploid cell resulting from the fertilisation of haploid gametes from the male and female lines.