Medically Reviewed by Dan Brennan, MD on June 05, 2021 Your body must stick to a precise balance of acidity and alkalinity in order to function properly. Even a slight change in this balance can affect many organs. The acidity and alkalinity of your blood are measured using the pH scale. The pH scale ranges from 0 (very acidic) to 14 (very alkaline). Blood is usually between 7.35 to 7.45. Every organ system in your body depends on pH balance. But your lungs and kidneys work to regulate it. Acids are produced during the many chemical reactions that take place in each cell (cellular metabolism). Carbon dioxide is constantly being produced by your cells as they metabolize the oxygen and nutrients they need. Each time there’s a change in the acid-base balance, your body automatically pushes your blood pH level back to normal. But if your blood pH level changes significantly, then these automatic mechanisms aren’t working. Lungs. Your brain controls how fast and how deeply you breathe. It regulates the amount of carbon dioxide you’re breathing out. When you breathe deeper and faster, you exhale more carbon dioxide and increase the pH of your blood. Your breathing, or respiratory, system can adjust the pH level of your blood in just minutes. Kidneys. Your renal system can also adjust your blood pH level. Your kidneys are able to remove excess acids or bases. But this effect can take hours or days. Chemical buffer systems. Your body also has chemical buffer systems — built-in weak acids and bases — that can easily be broken down. They work by adjusting your body’s proportions of acids and bases. Your body’s other chemical systems involve proteins, hemoglobin, and phosphates. The phosphate buffer system helps regulate the pH level of your urine. Proteins help with pH regulation within cells. Hemoglobin, the main protein inside your red blood cells, helps regulate pH there. Your blood may have too much acid. This results in acidosis. When your blood has too much base (too alkaline), this is known as alkalosis. Acidosis and alkalosis aren’t diseases, but they provide health care professionals with a clue that you may have a serious health problem. Respiratory acidosis. This happens when your lungs aren’t able to remove excess carbon dioxide, and it builds up in your body. The causes of respiratory acidosis include: Early symptoms of respiratory acidosis include: Metabolic acidosis. This happens when your body produces too much acid or is unable to remove acids properly. Causes of metabolic acidosis include: If your metabolic acidosis is mild, you may not have any symptoms. Otherwise, you may experience: How your body responds to acidosis may leave you feeling weak, drowsy, and confused. In severe cases, you may develop heart problems and a drop in blood pressure. This can lead to coma and death. This is when your body: Respiratory alkalosis. This may be caused by hyperventilation or rapid breathing. Such breathing causes too much carbon dioxide to be removed from your body. Hyperventilation may be due to: Metabolic alkalosis. This may be caused by: Symptoms of alkalosis include: Sometimes alkalosis may not cause any symptoms. Your doctor may order blood tests to measure the pH and carbon dioxide levels in your blood. The blood sample is usually taken from an artery in your wrist. Blood from your veins isn’t as reliable as arterial blood when measuring blood pH. For acidosis, your doctor may also measure the amount of bicarbonate in your blood. Other blood tests may be needed to find out the cause of your acidosis. For alkalosis, your doctor may also measure electrolyte levels in your blood and urine. Your doctor will work on reversing the cause of your acidosis or alkalosis. For metabolic acidosis, treatment depends on the cause. For example, your doctor may treat your Type 1 diabetes. If you have respiratory acidosis, your doctor will work on improving your lung function. You may need drugs that open your airways. If your breathing is badly impaired, you may need a mechanical ventilator to help you breathe. For metabolic alkalosis, you may be given water and electrolytes while the cause is treated. For respiratory alkalosis, the first step is to give oxygen. Your doctor will then look for the cause and treat it.
By the end of this section, you will be able to:
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 26.4.1. 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.  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 from the body. The renal system can also adjust blood pH through the excretion of hydrogen ions (H+) and the conservation of bicarbonate, but this process takes hours to days to have an effect. 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. 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. Hemoglobin 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 into bicarbonate, hydrogen ions liberated in the reaction are buffered by hemoglobin, 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, 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. Phosphates are found in the blood in two forms: sodium dihydrogen phosphate (Na2H2PO4−), which is a weak acid, and sodium monohydrogen phosphate (Na2HPO42-), which is a weak base. When Na2HPO42- comes into contact with a strong acid, such as HCl, the base picks up a second hydrogen ion to form the weak acid Na2H2PO4− and sodium chloride, NaCl. When Na2HPO42− (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. HCl + Na2HPO4→NaH2PO4 + NaCl
(strong acid) + (weak base) → (weak acid) + (salt)
NaOH + NaH2PO4→Na2HPO4 + H2O
(strong base) + (weak acid) → (weak base) + (water) 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), comes into contact with a strong acid, such as HCl, carbonic acid (H2CO3), 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. NaHCO3 + HCl → H2CO3+NaCl (sodium bicarbonate) + (strong acid) → (weak acid) + (salt) (weak acid) + (strong base)→(bicarbonate) + (water) 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’s metabolic wastes, such as lactic acid and ketones, are acids. Carbonic acid levels in the blood are controlled by the expiration of CO2 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 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. CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3– **EDITOR’S NOTE: Add a figure similar to Marieb 26.12 from 10th edition The respiratory system contributes to the balance of acids and bases in the body by regulating the blood levels of carbonic acid (Figure 26.4.2). CO2 in the blood readily reacts with water to form carbonic acid, and the levels of CO2 and carbonic acid in the blood are in equilibrium. When the CO2 level in the blood rises (as it does when you hold your breath), the excess CO2 reacts with water to form additional carbonic acid, lowering blood pH. Increasing the rate and/or depth of respiration (which you might feel the “urge” to do after holding your breath) allows you to exhale more CO2. The loss of CO2 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 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. The chemical reactions that regulate the levels of CO2 and carbonic acid occur in the lungs when blood travels through the lung’s pulmonary capillaries. Minor adjustments in breathing are usually sufficient to adjust the pH of the blood by changing how much CO2 is exhaled. In fact, doubling the respiratory rate for less than 1 minute, removing “extra” CO2, 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 (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. This helps to keep you from developing acidosis. The body regulates the respiratory rate by the use of chemoreceptors, which primarily use CO2 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 levels rise or fall. Yet other sensors are found in the brain itself. Changes in the pH of CSF affect the respiratory center in the medulla oblongata, which can directly modulate breathing rate to bring the pH back into the normal range. Hypercapnia, or abnormally elevated blood levels of CO2, 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’s breath) can also result in hypercapnia. Hypocapnia, or abnormally low blood levels of CO2, occurs with any cause of hyperventilation that drives off the CO2, such as salicylate toxicity, elevated room temperatures, fever, or hysteria. The renal regulation of the body’s acid-base balance addresses the metabolic component of the buffering system. Whereas the respiratory system (together with breathing centers in the brain) controls the blood levels of carbonic acid by controlling the exhalation of CO2, 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 diarrhea. Blood bicarbonate levels are also typically lower in people who have Addison’s 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. Bicarbonate ions, HCO3–, 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 26.4.3 and are summarized below:
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. In such cases, bicarbonate ions are not conserved from the filtrate to the blood, which will also contribute to a pH imbalance and acidosis. 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 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. Chloride ions are important in neutralizing 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.
Acid-Base Balance: KetoacidosisDiabetic 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’t supplied with enough of its fuel—glucose—to produce all of the ATP it requires to function. 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 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. Among people with type 2 diabetes, those of Hispanic and African-American descent are more likely to go into ketoacidosis than those of other ethnic backgrounds, although the reason for this is unknown.
A variety of buffering systems exist in the body that helps maintain the pH of the blood and other fluids within a narrow range—between 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–), or a weak base, which takes up a hydrogen ion (H+). Several substances serve as buffers in the body, including cell and plasma proteins, hemoglobin, 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 and hydrogen ions, respectively, from the body. hypercapnia abnormally elevated blood levels of CO2 hypocapnia abnormally low blood levels of CO2 |
What method is used to assess the acid-base balance of the body?
Related Posts
Copyright © 2024 ShotOnMac Inc.
