Acid–base physiology

The body is able to maintain an arterial pH in a very narrow range due to intracellular and extracellular mechanisms that are able to correct for large physiologic perturbations. The most common mechanisms for compensation of pH abnormalities is through the respiratory and renal systems which alter carbon dioxide (CO₂) and bicarbonate (HCO₃^-) resorption and excretion. Carbon dioxide, a volatile acid, is a byproduct of cellular aerobic respiration that combines with water to form carbonic acid (H₂CO₃) which can be catalyzed by carbonic anhydrase to produce protons (H⁺) and bicarbonate (HCO₃^-Nonvolatile acids can be produced from protein catabolism as seen with sulfuric acid (H₂SO₄), phospholipid breakdown as seen with phosphoric acid (H₃PO₄), as a byproduct of anaerobic respiration as is the case with lactic acid, or as a result of a disease process such as that seen with ketoacid production in patients with diabetes. Buffering solutions, weak acids or bases and their conjugate bases and acids, respectively, are the first line of defense against significant changes in the pH. These can be found, both in extracellular fluid, or within cells themselves. Most common extracellular buffers include the bicarbonate and carbon dioxide system described above. Other buffering systems, such as Phosphates, Intracellular Proteins, and Hemoglobin, also exist but have a less profound impact upon the maintenance of pH.