How does the body regulate acid-base balance?
Answer
There are three regulatory systems of acid-base balance: 1. Buffers 2. Lungs 3. Kidneys. The Henderson-Hasselbach equation gives us the pH of a solution.
pH = pk + log [A-/HA] increase [H+] = pH decreases ==> acidosis decrease [H+] = pH increases ==>alkalosis pH of normal blood = 7.4
pH = 6.1 + log [HCO3- / 0.03 * PaCo2] The PaCO2 is what the lungs regulate.
The body must maintain PaO2 and PaCO2. There are central and peripheral chemoreceptors working with it. The central chemoreceptors include the brain and brainstem. In contrast, the peripheral chemoreceptors include the aortic body and carotid body. Peripheral chemoreceptors monitor PaO2, [H+], and pH of blood. CO2 levels in the blood depend on how many are produced, and how many are in the blood. The brainstem senses the chemosensitive area [H+] in CSF. Hydrogen ions [H+] cannot cross the blood-brain barrier but CO2 can. If PaCO2 levels are high CO2 crosses the BBB ==>CO2 + H2O ==> H2CO3 ==> H+ +HCO3-. These H+ triggers the inspiratory center which increases alveolar ventilation. There is the removal of excess CO2 that lowers the H+ and normalizing pH. This takes about 1-2 days when the kidneys take over. The kidneys increase H+ excretion and increase (bicarb) HCO3- reabsorption
Decreased pH = pK + log [HCO3-/ 0.03 * PaCO2 increases] The kidneys compensate by increasing HCO3-.
Increased pH = pK + log [HCO3-/ 0.03 * PaCO2 decrease] The kidneys compensate by lowering HCO3-.
The four stages of acid-base balance are respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis. Respiratory acidosis can be caused by hypoventilation. There is increased CO2 retention. PaCO2 would be increased; pH decreased; the kidneys compensate by increasing HCO3-==> this is metabolic compensation for respiratory acidosis.
Respiratory alkalosis can be caused by hyperventilation. There is more CO2 washout causing PaCO2 decreases and increases pH. The compensation is through the kidneys where they lower HCO3-. This is metabolic compensation for respiratory alkalosis.
Metabolic acidosis changes in the pH of blood are detected by peripheral chemoreceptors in carotid bodies. If pH is low, it stimulates the receptors which stimulates center for inspiration which increases ventilation. More CO2 washout. This is the respiratory compensation for metabolic acidosis.
Metabolic alkalosis occurs when pH is high. The chemoreceptors are stimulated and the center for inspiration reduces ventilation which further increases CO2 retention. This is the respiratory compensation for metabolic alkalosis.
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