Renal physiology: acid-base balance

Acid-base balance is a fundamental part of human homeostasis. The human body has evolved a system which allows exquisite control, involving multi-organ systems, over the pH of the intracellular and extracellular fluid. The Henderson-Hasselbalch equation relates pH to the dissociation constant, pKa, and relative concentrations of dissociated and undissociated acid. One of the clinical applications of this equation is in the use of local anaesthetic agents, applying knowledge of pH and pKa to select the most appropriate drug. In order to exert such fine control over pH, buffer systems exist that rapidly permit correction of any deviance outside the normal range. The principal buffer system is the bicarbonate buffer system, mediated through carbonic anhydrase. The renal system exerts control over the ultimate fate of bicarbonate and hydrogen ions through a series of chemical reactions, culminating in the excretion of excess acid or base. Abnormalities in acid-base balance can have profound consequences and it is therefore vital to understand the basis of the abnormality in order to effectively treat the condition.