Overview of Acid–Base Physiology

Abstract

Maintenance of normal acid–base homeostasis is critical to optimal cell, organ, and whole-body function. Multiple and redundant systems, importantly those in the liver, lungs, and kidneys, work to maintain this homeostasis in the face of continuous challenges from routine metabolic processes, diet, physical activity, and illness. The liver metabolizes substances, including those ingested in the diet, to yield acid, base, or neither. The lung’s major contribution to acid–base homeostasis is excretion of “volatile” acid (carbon dioxide or CO₂) whose retention increases the respiratory component of the acid–base equilibrium to cause “respiratory” acidosis. The kidney’s major contribution to this process is excretion of so-called fixed acid whose retention lowers the metabolic component of the acid–base equilibrium (bicarbonate or HCO₃), causing “metabolic” acidosis. Here we provide a general overview of overall acid–base homeostasis with particular emphasis on the kidney given its important role in protecting against and sometimes causing metabolic acidosis.