Clinical Correlates

Acid–base disturbances occur under a variety of conditions. Hypoventilation causes retention of CO2 by the lungs, which can lead to a respiratory acidosis. Hyperventilation can cause a respiratory alkalosis. Metabolic acidosis can result from accumulation of metabolic acids (lactic acid or the ketone bodies, β-hydroxybutyric acid and acetoacetic acid), or ingestion of acids or compounds that are metabolized to acids (e.g., methanol, ethylene glycol).

Metabolic alkalosis is due to increased HCO3?, which is accompanied by an increased pH. Acid–base disturbances lead to compensatory responses that attempt to restore the normal pH. For example, a metabolic acidosis causes hyperventilation and the release of CO2, which tends to lower the pH. During metabolic acidosis, the kidneys excrete NH4+, which contains H+ buffered by ammonia.

Failure of the gastroesophageal sphincter can lead to gastric reflux disease, in which the acid (HCl) contents of the stomach travel up the esophagus. The consequences of this disorder (esophageal damage due to acid refluxing up into the esophagus) can be treated, in part, by use of drugs that inhibit the gastric proton-translocating H+/K+ ATPase of the parietal cells, which pumps protons into the stomach lumen (in exchange for K+ outside the cell) against a concentration gradient using the energy of ATP. The use of these drugs increases the pH of the stomach contents, which lessens esophageal damage and allows the tissue to heal.