{"id":1188,"date":"2021-01-28T01:54:02","date_gmt":"2021-01-28T01:54:02","guid":{"rendered":"https:\/\/pressbooks.publishdot.com\/anatomyphysiology\/chapter\/17-14-acid-base-balance\/"},"modified":"2021-12-07T10:42:07","modified_gmt":"2021-12-07T10:42:07","slug":"17-14-acid-base-balance","status":"publish","type":"chapter","link":"https:\/\/pressbooks.publishdot.com\/anatomyphysiology\/chapter\/17-14-acid-base-balance\/","title":{"raw":"17.14 Acid-Base Balance","rendered":"17.14 Acid-Base Balance"},"content":{"raw":"
\n

Learning Objectives<\/strong><\/p>\n\n<\/header>\n

\n\nBy the end of this section, you will be able to:\n
    \n \t
  • Identify the most powerful buffer system in the body<\/li>\n \t
  • Explain the way in which the respiratory system affects blood pH<\/li>\n<\/ul>\n<\/div>\n<\/div>\nProper physiological functioning depends on a very tight balance between the concentrations of acids and bases in the blood. Acid-balance balance is measured using the pH scale, as shown in Figure 17.14.1. A variety of buffering systems permits blood and other bodily fluids to maintain a narrow pH range, even in the face of perturbations. A buffer is a chemical system that prevents a radical change in fluid pH by dampening the change in hydrogen ion concentrations in the case of excess acid or base. Most commonly, the substance that absorbs the ions is either a weak acid, which takes up hydroxyl ions, or a weak base which takes up hydrogen ions.\n\n \n\n[caption id=\"attachment_1187\" align=\"aligncenter\" width=\"597\"]\"The Figure 17.14.1. The pH scale.<\/strong> This chart shows where many common substances fall on the pH scale.[\/caption]\n

    Buffer Systems in the Body<\/h2>\nThe buffer systems in the human body are extremely efficient and different systems work at different rates. It takes only seconds for the chemical buffers in the blood to make adjustments to pH. The respiratory tract can adjust the blood pH upward in minutes by exhaling CO2<\/sub> from the body. The renal system can also adjust blood pH through the excretion of hydrogen ions (H+<\/sup>) and the conservation of bicarbonate, but this process takes hours to days to have an effect.\n\nThe buffer systems functioning in blood plasma include plasma proteins, phosphate and bicarbonate and carbonic acid buffers. The kidneys help control acid-base balance by excreting hydrogen ions and generating bicarbonate that helps maintain blood plasma pH within a normal range. Protein buffer systems work predominantly inside cells.\n

    Protein Buffers in Blood Plasma and Cells<\/h2>\nNearly all proteins can function as buffers. Proteins are made up of amino acids, which contain positively charged amino groups and negatively charged carboxyl groups. The charged regions of these molecules can bind hydrogen and hydroxyl ions, and thus function as buffers. Buffering by proteins accounts for two-thirds of the buffering power of the blood and most of the buffering within cells.\n

    Haemoglobin as a Buffer<\/h2>\nHaemoglobin is the principal protein inside of red blood cells and accounts for one-third of the mass of the cell. During the conversion of CO2<\/sub> into bicarbonate, hydrogen ions liberated in the reaction are buffered by haemoglobin, which is reduced by the dissociation of oxygen. This buffering helps maintain normal pH. The process is reversed in the pulmonary capillaries to re-form CO2<\/sub>, which then can diffuse into the air sacs to be exhaled into the atmosphere. This process is discussed in detail in the chapter on the respiratory system.\n

    Phosphate Buffer<\/h2>\nPhosphates are found in the blood in two forms: sodium dihydrogen phosphate (Na2<\/sub>H2<\/sub>PO4<\/sub>\u2212<\/sup>), which is a weak acid, and sodium monohydrogen phosphate (Na2<\/sub>HPO4<\/sub>2-<\/sup>), which is a weak base. When Na2<\/sub>HPO4<\/sub>2-<\/sup> comes into contact with a strong acid, such as HCl, the base picks up a second hydrogen ion to form the weak acid Na2<\/sub>H2<\/sub>PO4<\/sub>\u2212<\/sup> and sodium chloride, NaCl. When Na2<\/sub>HPO4<\/sub>2\u2212<\/sup> (the weak acid) comes into contact with a strong base, such as sodium hydroxide (NaOH), the weak acid reverts back to the weak base and produces water. Acids and bases are still present, but they hold onto the ions.\n\nHCl + Na2<\/sub>HPO4<\/sub>\u2192NaH2<\/sub>PO4<\/sub> + NaCl\n\n(strong acid) + (weak base) \u2192 (weak acid) + (salt)\n\nNaOH + NaH2<\/sub>PO4<\/sub>\u2192Na2<\/sub>HPO4<\/sub> + H2<\/sub>O\n\n(strong base) + (weak acid) \u2192 (weak base) + (water)\n

    Bicarbonate-Carbonic Acid Buffer<\/h2>\nThe bicarbonate-carbonic acid buffer works in a fashion similar to phosphate buffers. The bicarbonate is regulated in the blood by sodium, as are the phosphate ions. When sodium bicarbonate (NaHCO3<\/sub>), comes into contact with a strong acid, such as HCl, carbonic acid (H2<\/sub>CO3<\/sub>), which is a weak acid, and NaCl are formed. When carbonic acid comes into contact with a strong base, such as NaOH, bicarbonate and water are formed.\n\nNaHCO3<\/sub> + HCl \u2192\u00a0 H2<\/sub>CO3<\/sub>+NaCl\n\n(sodium bicarbonate) + (strong acid) \u2192 (weak acid) + (salt)\n\nH2<\/sub>CO3<\/sub> + NaOH\u2192HCO3<\/sub>- + H2<\/sub>O\n\n(weak acid) + (strong base)\u2192(bicarbonate) + (water)\n\nAs with the phosphate buffer, a weak acid or weak base captures the free ions, and a significant change in pH is prevented. Bicarbonate ions and carbonic acid are present in the blood in a 20:1 ratio if the blood pH is within the normal range. With 20 times more bicarbonate than carbonic acid, this capture system is most efficient at buffering changes that would make the blood more acidic. This is useful because most of the body\u2019s metabolic wastes, such as lactic acid and ketones, are acids. Carbonic acid levels in the blood are controlled by the expiration of CO2<\/sub> through the lungs. In red blood cells, carbonic anhydrase forces the dissociation of the acid, rendering the blood less acidic. Because of this acid dissociation, CO2<\/sub> is exhaled (see equations above). The level of bicarbonate in the blood is controlled through the renal system, where bicarbonate ions in the renal filtrate are conserved and passed back into the blood. However, the bicarbonate buffer is the primary buffering system of the IF surrounding the cells in tissues throughout the body.\n

    Respiratory Regulation of Acid-Base Balance<\/h2>\nThe respiratory system contributes to the balance of acids and bases in the body by regulating the blood levels of carbonic acid (Figure 17.14.2). CO2<\/sub> in the blood readily reacts with water to form carbonic acid, and the levels of CO2<\/sub> and carbonic acid in the blood are in equilibrium. When the CO2<\/sub> level in the blood rises (as it does when you hold your breath), the excess CO2<\/sub> reacts with water to form additional carbonic acid, lowering blood pH. Increasing the rate and\/or depth of respiration (which you might feel the \u201curge\u201d to do after holding your breath) allows you to exhale more CO2<\/sub>. The loss of CO2<\/sub> from the body reduces blood levels of carbonic acid and thereby adjusts the pH upward, toward normal levels. As you might have surmised, this process also works in the opposite direction. Excessive deep and rapid breathing (as in hyperventilation) rids the blood of CO2<\/sub> and reduces the level of carbonic acid, making the blood too alkaline. This brief alkalosis can be remedied by rebreathing air that has been exhaled into a paper bag. Rebreathing exhaled air will rapidly bring blood pH down toward normal.\n\n \n\n[caption id=\"attachment_1187\" align=\"aligncenter\" width=\"495\"]\"flowchart Figure 17.14.2. Respiratory regulation of blood pH.<\/strong> The respiratory system can reduce blood pH by removing CO2<\/sub> from the blood.[\/caption]\n\nThe chemical reactions that regulate the levels of CO2<\/sub> and carbonic acid occur in the lungs when blood travels through the lung\u2019s pulmonary capillaries. Minor adjustments in breathing are usually sufficient to adjust the pH of the blood by changing how much CO2<\/sub> is exhaled. In fact, doubling the respiratory rate for less than 1 minute, removing \u201cextra\u201d CO2<\/sub>, would increase the blood pH by 0.2. This situation is common if you are exercising strenuously over a period of time. To keep up the necessary energy production, you would produce excess CO2<\/sub> (and lactic acid if exercising beyond your aerobic threshold). In order to balance the increased acid production, the respiration rate goes up to remove the CO2<\/sub>. This helps to keep you from developing acidosis.\n\nThe body regulates the respiratory rate by the use of chemoreceptors, which primarily use CO2<\/sub> as a signal. Peripheral blood sensors are found in the walls of the aorta and carotid arteries. These sensors signal the brain to provide immediate adjustments to the respiratory rate if CO2<\/sub> levels rise or fall. Yet other sensors are found in the brain itself. Changes in the pH of CSF affect the respiratory centre in the medulla oblongata, which can directly modulate breathing rate to bring the pH back into the normal range.\n\nHypercapnia<\/strong>, or abnormally elevated blood levels of CO2<\/sub>, occurs in any situation that impairs respiratory functions, including pneumonia and congestive heart failure. Reduced breathing (hypoventilation) due to drugs such as morphine, barbiturates or ethanol (or even just holding one\u2019s breath) can also result in hypercapnia. Hypocapnia<\/strong>, or abnormally low blood levels of CO2<\/sub>, occurs with any cause of hyperventilation that drives off the CO2<\/sub>, such as salicylate toxicity, elevated room temperatures, fever or hysteria.\n

    Renal Regulation of Acid-Base Balance<\/h2>\nThe renal regulation of the body\u2019s acid-base balance addresses the metabolic component of the buffering system. Whereas the respiratory system (together with breathing centres in the brain) controls the blood levels of carbonic acid by controlling the exhalation of CO2<\/sub>, the renal system controls the blood levels of bicarbonate. A decrease of blood bicarbonate can result from the inhibition of carbonic anhydrase by certain diuretics or from excessive bicarbonate loss due to diarrhoea. Blood bicarbonate levels are also typically lower in people who have Addison\u2019s disease (chronic adrenal insufficiency), in which aldosterone levels are reduced, and in people who have renal damage, such as chronic nephritis. Finally, low bicarbonate blood levels can result from elevated levels of ketones (common in unmanaged diabetes mellitus), which bind bicarbonate in the filtrate and prevent its conservation.\n\nBicarbonate ions, HCO3<\/sub>\u2013<\/sup>, found in the filtrate, are essential to the bicarbonate buffer system, yet the cells of the tubule are not permeable to bicarbonate ions. The steps involved in supplying bicarbonate ions to the system are seen in Figure 17.14.3 and are summarised below:\n\nStep 1: <\/strong>Sodium ions are reabsorbed from the filtrate in exchange for H+<\/sup> by an antiport mechanism in the apical membranes of cells lining the renal tubule.\n\nStep 2:<\/strong> The cells produce bicarbonate ions that can be shunted to peritubular capillaries.\n\nStep 3:<\/strong> When CO2<\/sub> is available, the reaction is driven to the formation of carbonic acid, which dissociates to form a bicarbonate ion and a hydrogen ion.\n\nStep 4: <\/strong>The bicarbonate ion passes into the peritubular capillaries and returns to the blood. The hydrogen ion is secreted into the filtrate, where it can become part of new water molecules and be reabsorbed as such or removed in the urine.\n\n[caption id=\"attachment_1187\" align=\"aligncenter\" width=\"1024\"]\"Conservation Figure 17.14.3. Conservation of bicarbonate in the kidney.<\/strong> Tubular cells are not permeable to bicarbonate; thus, bicarbonate is conserved rather than reabsorbed. Steps 1 and 2 of bicarbonate conservation are indicated.[\/caption]\n\nIt is also possible that salts in the filtrate, such as sulfates, phosphates, or ammonia, will capture hydrogen ions. If this occurs, the hydrogen ions will not be available to combine with bicarbonate ions and produce CO2<\/sub>. In such cases, bicarbonate ions are not conserved from the filtrate to the blood, which will also contribute to a pH imbalance and acidosis.\n\nThe hydrogen ions also compete with potassium to exchange with sodium in the renal tubules. If more potassium is present than normal, potassium, rather than the hydrogen ions, will be exchanged, and increased potassium enters the filtrate. When this occurs, fewer hydrogen ions in the filtrate participate in the conversion of bicarbonate into CO2<\/sub> and less bicarbonate is conserved. If there is less potassium, more hydrogen ions enter the filtrate to be exchanged with sodium and more bicarbonate is conserved.\n\nChloride ions are important in neutralising positive ion charges in the body. If chloride is lost, the body uses bicarbonate ions in place of the lost chloride ions. Thus, lost chloride results in an increased reabsorption of bicarbonate by the renal system.\n

    Disorders of the Acid-Base Balance: Ketoacidosis<\/h2>\nDiabetic acidosis, or ketoacidosis, occurs most frequently in people with poorly controlled diabetes mellitus. When certain tissues in the body cannot get adequate amounts of glucose, they depend on the breakdown of fatty acids for energy. When acetyl groups break off the fatty acid chains, the acetyl groups then non-enzymatically combine to form ketone bodies, acetoacetic acid, beta-hydroxybutyric acid and acetone, all of which increase the acidity of the blood. In this condition, the brain isn\u2019t supplied with enough of its fuel\u2014glucose\u2014to produce all of the ATP it requires to function.\n\nKetoacidosis can be severe and, if not detected and treated properly, can lead to diabetic coma, which can be fatal. A common early symptom of ketoacidosis is deep, rapid breathing as the body attempts to drive off CO2<\/sub> and compensate for the acidosis. Another common symptom is fruity-smelling breath, due to the exhalation of acetone. Other symptoms include dry skin and mouth, a flushed face, nausea, vomiting and stomach pain. Treatment for diabetic coma is ingestion or injection of sugar; its prevention is the proper daily administration of insulin. A person who is diabetic and uses insulin can initiate ketoacidosis if a dose of insulin is missed. Between 2014 and 2015, there were over 7,000 hospitalisations due to diabetic ketoacidosis in Australia, with approximately 85% of patients suffering from type I diabetes. Approximately half of these patients were children and young adults (under 25 years old).\n
    \n

    Section Review<\/strong><\/p>\n\n<\/header>\n

    \n\nA variety of buffering systems exist in the body that helps maintain the pH of the blood and other fluids within a narrow range\u2014between pH 7.35 and 7.45. A buffer is a substance that prevents a radical change in fluid pH by absorbing excess hydrogen or hydroxyl ions. Most commonly, the substance that absorbs the ion is either a weak acid, which takes up a hydroxyl ion (OH\u2013<\/sup>), or a weak base which takes up a hydrogen ion (H+<\/sup>). Several substances serve as buffers in the body, including cell and plasma proteins, haemoglobin, phosphates, bicarbonate ions and carbonic acid. The bicarbonate buffer is the primary buffering system of the IF surrounding the cells in tissues throughout the body. The respiratory and renal systems also play major roles in acid-base homeostasis by removing CO2<\/sub> and hydrogen ions, respectively, from the body.\n\n<\/div>\n<\/div>\n
    \n

    Review Questions<\/strong><\/p>\n\n<\/header>\n

    \n\n[h5p id=\"667\"]\n\n<\/div>\n<\/div>\n
    \n

    Critical Thinking Questions<\/strong><\/p>\n\n<\/header>\n

    \n\n[h5p id=\"668\"]\n\n[h5p id=\"669\"]\n\n<\/div>\n<\/div>\nClick the drop down below to review the terms learned from this chapter.\n\n[h5p id=\"670\"]","rendered":"
    \n
    \n

    Learning Objectives<\/strong><\/p>\n<\/header>\n

    \n

    By the end of this section, you will be able to:<\/p>\n

      \n
    • Identify the most powerful buffer system in the body<\/li>\n
    • Explain the way in which the respiratory system affects blood pH<\/li>\n<\/ul>\n<\/div>\n<\/div>\n

      Proper physiological functioning depends on a very tight balance between the concentrations of acids and bases in the blood. Acid-balance balance is measured using the pH scale, as shown in Figure 17.14.1. A variety of buffering systems permits blood and other bodily fluids to maintain a narrow pH range, even in the face of perturbations. A buffer is a chemical system that prevents a radical change in fluid pH by dampening the change in hydrogen ion concentrations in the case of excess acid or base. Most commonly, the substance that absorbs the ions is either a weak acid, which takes up hydroxyl ions, or a weak base which takes up hydrogen ions.<\/p>\n

       <\/p>\n

      \"The
      Figure 17.14.1. The pH scale.<\/strong> This chart shows where many common substances fall on the pH scale.<\/figcaption><\/figure>\n

      Buffer Systems in the Body<\/h2>\n

      The buffer systems in the human body are extremely efficient and different systems work at different rates. It takes only seconds for the chemical buffers in the blood to make adjustments to pH. The respiratory tract can adjust the blood pH upward in minutes by exhaling CO2<\/sub> from the body. The renal system can also adjust blood pH through the excretion of hydrogen ions (H+<\/sup>) and the conservation of bicarbonate, but this process takes hours to days to have an effect.<\/p>\n

      The buffer systems functioning in blood plasma include plasma proteins, phosphate and bicarbonate and carbonic acid buffers. The kidneys help control acid-base balance by excreting hydrogen ions and generating bicarbonate that helps maintain blood plasma pH within a normal range. Protein buffer systems work predominantly inside cells.<\/p>\n

      Protein Buffers in Blood Plasma and Cells<\/h2>\n

      Nearly all proteins can function as buffers. Proteins are made up of amino acids, which contain positively charged amino groups and negatively charged carboxyl groups. The charged regions of these molecules can bind hydrogen and hydroxyl ions, and thus function as buffers. Buffering by proteins accounts for two-thirds of the buffering power of the blood and most of the buffering within cells.<\/p>\n

      Haemoglobin as a Buffer<\/h2>\n

      Haemoglobin is the principal protein inside of red blood cells and accounts for one-third of the mass of the cell. During the conversion of CO2<\/sub> into bicarbonate, hydrogen ions liberated in the reaction are buffered by haemoglobin, which is reduced by the dissociation of oxygen. This buffering helps maintain normal pH. The process is reversed in the pulmonary capillaries to re-form CO2<\/sub>, which then can diffuse into the air sacs to be exhaled into the atmosphere. This process is discussed in detail in the chapter on the respiratory system.<\/p>\n

      Phosphate Buffer<\/h2>\n

      Phosphates are found in the blood in two forms: sodium dihydrogen phosphate (Na2<\/sub>H2<\/sub>PO4<\/sub>\u2212<\/sup>), which is a weak acid, and sodium monohydrogen phosphate (Na2<\/sub>HPO4<\/sub>2-<\/sup>), which is a weak base. When Na2<\/sub>HPO4<\/sub>2-<\/sup> comes into contact with a strong acid, such as HCl, the base picks up a second hydrogen ion to form the weak acid Na2<\/sub>H2<\/sub>PO4<\/sub>\u2212<\/sup> and sodium chloride, NaCl. When Na2<\/sub>HPO4<\/sub>2\u2212<\/sup> (the weak acid) comes into contact with a strong base, such as sodium hydroxide (NaOH), the weak acid reverts back to the weak base and produces water. Acids and bases are still present, but they hold onto the ions.<\/p>\n

      HCl + Na2<\/sub>HPO4<\/sub>\u2192NaH2<\/sub>PO4<\/sub> + NaCl<\/p>\n

      (strong acid) + (weak base) \u2192 (weak acid) + (salt)<\/p>\n

      NaOH + NaH2<\/sub>PO4<\/sub>\u2192Na2<\/sub>HPO4<\/sub> + H2<\/sub>O<\/p>\n

      (strong base) + (weak acid) \u2192 (weak base) + (water)<\/p>\n

      Bicarbonate-Carbonic Acid Buffer<\/h2>\n

      The bicarbonate-carbonic acid buffer works in a fashion similar to phosphate buffers. The bicarbonate is regulated in the blood by sodium, as are the phosphate ions. When sodium bicarbonate (NaHCO3<\/sub>), comes into contact with a strong acid, such as HCl, carbonic acid (H2<\/sub>CO3<\/sub>), which is a weak acid, and NaCl are formed. When carbonic acid comes into contact with a strong base, such as NaOH, bicarbonate and water are formed.<\/p>\n

      NaHCO3<\/sub> + HCl \u2192\u00a0 H2<\/sub>CO3<\/sub>+NaCl<\/p>\n

      (sodium bicarbonate) + (strong acid) \u2192 (weak acid) + (salt)<\/p>\n

      H2<\/sub>CO3<\/sub> + NaOH\u2192HCO3<\/sub>– + H2<\/sub>O<\/p>\n

      (weak acid) + (strong base)\u2192(bicarbonate) + (water)<\/p>\n

      As with the phosphate buffer, a weak acid or weak base captures the free ions, and a significant change in pH is prevented. Bicarbonate ions and carbonic acid are present in the blood in a 20:1 ratio if the blood pH is within the normal range. With 20 times more bicarbonate than carbonic acid, this capture system is most efficient at buffering changes that would make the blood more acidic. This is useful because most of the body\u2019s metabolic wastes, such as lactic acid and ketones, are acids. Carbonic acid levels in the blood are controlled by the expiration of CO2<\/sub> through the lungs. In red blood cells, carbonic anhydrase forces the dissociation of the acid, rendering the blood less acidic. Because of this acid dissociation, CO2<\/sub> is exhaled (see equations above). The level of bicarbonate in the blood is controlled through the renal system, where bicarbonate ions in the renal filtrate are conserved and passed back into the blood. However, the bicarbonate buffer is the primary buffering system of the IF surrounding the cells in tissues throughout the body.<\/p>\n

      Respiratory Regulation of Acid-Base Balance<\/h2>\n

      The respiratory system contributes to the balance of acids and bases in the body by regulating the blood levels of carbonic acid (Figure 17.14.2). CO2<\/sub> in the blood readily reacts with water to form carbonic acid, and the levels of CO2<\/sub> and carbonic acid in the blood are in equilibrium. When the CO2<\/sub> level in the blood rises (as it does when you hold your breath), the excess CO2<\/sub> reacts with water to form additional carbonic acid, lowering blood pH. Increasing the rate and\/or depth of respiration (which you might feel the \u201curge\u201d to do after holding your breath) allows you to exhale more CO2<\/sub>. The loss of CO2<\/sub> from the body reduces blood levels of carbonic acid and thereby adjusts the pH upward, toward normal levels. As you might have surmised, this process also works in the opposite direction. Excessive deep and rapid breathing (as in hyperventilation) rids the blood of CO2<\/sub> and reduces the level of carbonic acid, making the blood too alkaline. This brief alkalosis can be remedied by rebreathing air that has been exhaled into a paper bag. Rebreathing exhaled air will rapidly bring blood pH down toward normal.<\/p>\n

       <\/p>\n

      \"flowchart
      Figure 17.14.2. Respiratory regulation of blood pH.<\/strong> The respiratory system can reduce blood pH by removing CO2<\/sub> from the blood.<\/figcaption><\/figure>\n

      The chemical reactions that regulate the levels of CO2<\/sub> and carbonic acid occur in the lungs when blood travels through the lung\u2019s pulmonary capillaries. Minor adjustments in breathing are usually sufficient to adjust the pH of the blood by changing how much CO2<\/sub> is exhaled. In fact, doubling the respiratory rate for less than 1 minute, removing \u201cextra\u201d CO2<\/sub>, would increase the blood pH by 0.2. This situation is common if you are exercising strenuously over a period of time. To keep up the necessary energy production, you would produce excess CO2<\/sub> (and lactic acid if exercising beyond your aerobic threshold). In order to balance the increased acid production, the respiration rate goes up to remove the CO2<\/sub>. This helps to keep you from developing acidosis.<\/p>\n

      The body regulates the respiratory rate by the use of chemoreceptors, which primarily use CO2<\/sub> as a signal. Peripheral blood sensors are found in the walls of the aorta and carotid arteries. These sensors signal the brain to provide immediate adjustments to the respiratory rate if CO2<\/sub> levels rise or fall. Yet other sensors are found in the brain itself. Changes in the pH of CSF affect the respiratory centre in the medulla oblongata, which can directly modulate breathing rate to bring the pH back into the normal range.<\/p>\n

      Hypercapnia<\/strong>, or abnormally elevated blood levels of CO2<\/sub>, occurs in any situation that impairs respiratory functions, including pneumonia and congestive heart failure. Reduced breathing (hypoventilation) due to drugs such as morphine, barbiturates or ethanol (or even just holding one\u2019s breath) can also result in hypercapnia. Hypocapnia<\/strong>, or abnormally low blood levels of CO2<\/sub>, occurs with any cause of hyperventilation that drives off the CO2<\/sub>, such as salicylate toxicity, elevated room temperatures, fever or hysteria.<\/p>\n

      Renal Regulation of Acid-Base Balance<\/h2>\n

      The renal regulation of the body\u2019s acid-base balance addresses the metabolic component of the buffering system. Whereas the respiratory system (together with breathing centres in the brain) controls the blood levels of carbonic acid by controlling the exhalation of CO2<\/sub>, the renal system controls the blood levels of bicarbonate. A decrease of blood bicarbonate can result from the inhibition of carbonic anhydrase by certain diuretics or from excessive bicarbonate loss due to diarrhoea. Blood bicarbonate levels are also typically lower in people who have Addison\u2019s disease (chronic adrenal insufficiency), in which aldosterone levels are reduced, and in people who have renal damage, such as chronic nephritis. Finally, low bicarbonate blood levels can result from elevated levels of ketones (common in unmanaged diabetes mellitus), which bind bicarbonate in the filtrate and prevent its conservation.<\/p>\n

      Bicarbonate ions, HCO3<\/sub>\u2013<\/sup>, found in the filtrate, are essential to the bicarbonate buffer system, yet the cells of the tubule are not permeable to bicarbonate ions. The steps involved in supplying bicarbonate ions to the system are seen in Figure 17.14.3 and are summarised below:<\/p>\n

      Step 1: <\/strong>Sodium ions are reabsorbed from the filtrate in exchange for H+<\/sup> by an antiport mechanism in the apical membranes of cells lining the renal tubule.<\/p>\n

      Step 2:<\/strong> The cells produce bicarbonate ions that can be shunted to peritubular capillaries.<\/p>\n

      Step 3:<\/strong> When CO2<\/sub> is available, the reaction is driven to the formation of carbonic acid, which dissociates to form a bicarbonate ion and a hydrogen ion.<\/p>\n

      Step 4: <\/strong>The bicarbonate ion passes into the peritubular capillaries and returns to the blood. The hydrogen ion is secreted into the filtrate, where it can become part of new water molecules and be reabsorbed as such or removed in the urine.<\/p>\n

      \"Conservation
      Figure 17.14.3. Conservation of bicarbonate in the kidney.<\/strong> Tubular cells are not permeable to bicarbonate; thus, bicarbonate is conserved rather than reabsorbed. Steps 1 and 2 of bicarbonate conservation are indicated.<\/figcaption><\/figure>\n

      It is also possible that salts in the filtrate, such as sulfates, phosphates, or ammonia, will capture hydrogen ions. If this occurs, the hydrogen ions will not be available to combine with bicarbonate ions and produce CO2<\/sub>. In such cases, bicarbonate ions are not conserved from the filtrate to the blood, which will also contribute to a pH imbalance and acidosis.<\/p>\n

      The hydrogen ions also compete with potassium to exchange with sodium in the renal tubules. If more potassium is present than normal, potassium, rather than the hydrogen ions, will be exchanged, and increased potassium enters the filtrate. When this occurs, fewer hydrogen ions in the filtrate participate in the conversion of bicarbonate into CO2<\/sub> and less bicarbonate is conserved. If there is less potassium, more hydrogen ions enter the filtrate to be exchanged with sodium and more bicarbonate is conserved.<\/p>\n

      Chloride ions are important in neutralising positive ion charges in the body. If chloride is lost, the body uses bicarbonate ions in place of the lost chloride ions. Thus, lost chloride results in an increased reabsorption of bicarbonate by the renal system.<\/p>\n

      Disorders of the Acid-Base Balance: Ketoacidosis<\/h2>\n

      Diabetic acidosis, or ketoacidosis, occurs most frequently in people with poorly controlled diabetes mellitus. When certain tissues in the body cannot get adequate amounts of glucose, they depend on the breakdown of fatty acids for energy. When acetyl groups break off the fatty acid chains, the acetyl groups then non-enzymatically combine to form ketone bodies, acetoacetic acid, beta-hydroxybutyric acid and acetone, all of which increase the acidity of the blood. In this condition, the brain isn\u2019t supplied with enough of its fuel\u2014glucose\u2014to produce all of the ATP it requires to function.<\/p>\n

      Ketoacidosis can be severe and, if not detected and treated properly, can lead to diabetic coma, which can be fatal. A common early symptom of ketoacidosis is deep, rapid breathing as the body attempts to drive off CO2<\/sub> and compensate for the acidosis. Another common symptom is fruity-smelling breath, due to the exhalation of acetone. Other symptoms include dry skin and mouth, a flushed face, nausea, vomiting and stomach pain. Treatment for diabetic coma is ingestion or injection of sugar; its prevention is the proper daily administration of insulin. A person who is diabetic and uses insulin can initiate ketoacidosis if a dose of insulin is missed. Between 2014 and 2015, there were over 7,000 hospitalisations due to diabetic ketoacidosis in Australia, with approximately 85% of patients suffering from type I diabetes. Approximately half of these patients were children and young adults (under 25 years old).<\/p>\n

      \n
      \n

      Section Review<\/strong><\/p>\n<\/header>\n

      \n

      A variety of buffering systems exist in the body that helps maintain the pH of the blood and other fluids within a narrow range\u2014between pH 7.35 and 7.45. A buffer is a substance that prevents a radical change in fluid pH by absorbing excess hydrogen or hydroxyl ions. Most commonly, the substance that absorbs the ion is either a weak acid, which takes up a hydroxyl ion (OH\u2013<\/sup>), or a weak base which takes up a hydrogen ion (H+<\/sup>). Several substances serve as buffers in the body, including cell and plasma proteins, haemoglobin, phosphates, bicarbonate ions and carbonic acid. The bicarbonate buffer is the primary buffering system of the IF surrounding the cells in tissues throughout the body. The respiratory and renal systems also play major roles in acid-base homeostasis by removing CO2<\/sub> and hydrogen ions, respectively, from the body.<\/p>\n<\/div>\n<\/div>\n

      \n
      \n

      Review Questions<\/strong><\/p>\n<\/header>\n

      \n
      \n