Urinary System

Acid-Base Physiology: Introduction and Index

Understanding acid-base homeostasis is most simply described as understanding how the concentration of hydrogen ions is regulated in physiologic systems. The normal concentration of free hydrogen ions (protons) inside and outside of cells is quite low - roughly 0.00000004 molar - but even small deviations in this concentration can have profound effects on biochemical processes and thereby on virtually all physiologic processes in the whole animal. Why? This is because a large number of molecules within and on the surface of cells (enzymes, for example) have evolved to function properly only within a very narrow range of hydrogen ion concentration.

Hydrogen ion concentration is usually described in terms of pH. Normal blood pH is roughly 7.4 and deviation in pH in either direction has profound effects on physiologic processes. Blood pH lower than 6.9 or higher than 7.7 is usually lethal, and disease ensues well before these extremes are reached. As you might expect, very sophisticated processes have evolved to prevent such deviations.

Acids and bases are generated continually through normal metabolism, with a relative overproduction of acid. Acid-base balance is therefore devoted to maintaining hydrogen ion concentration (i.e. pH) within a narrow range by eliminating excess acid (usually) or base (in some cases). This is accomplished through the cooperation of two organs:

Core concepts for the regulation of acid-base homeostasis

Advanced and supplemental topics on regulation of acid-base homeostasis:

Updated August 2019. Send comments to Richard.Bowen@colostate.edu