Acid–base balance: maintenance of plasma pH

Maintenance of the alkaline environment (pH∼7.4) of body fluids in the face of the production of vast quantities of acid as volatile acid (CO2) or non-volatile acids from metabolism requires defence mechanisms for both short- and long-term regulation. Short-term regulation is achieved through intracellular and extracellular buffer systems, with the main buffer system in plasma being H2CO3/HCO3– and the removal of CO2 through altered alveolar ventilation, but these can only limit the change in pH. Long-term regulation that can restore plasma pH involves regulation of renal tubular H+ secretion, the major determinant of HCO3– reabsorption, and the excretion of NH4+ and acid buffer salts, both of which result in HCO3– production by renal tubular cells. Disturbances in acid–base balance can be subdivided into those of either respiratory or metabolic (non-respiratory) origin and include both acidosis and alkalosis. As a general rule the effects of respiratory disturbances can be minimized by non-HCO3– buffer systems and corrected through changes in renal function, whereas the effects of metabolic disturbances are minimized by both HCO3– and non-HCO3– buffer systems and changes in alveolar ventilation and corrected through changes in renal function.