Acid–base homeostasis

Acid–base homeostasis is the part of biologic homeostasis (See The extracellular fluid pH homeostat) concerning the proper balance between chemical acids and bases, also called body pH. The body is very sensitive to its extracellular pH level, so strong mechanisms exist to maintain it. Outside the acceptable range of pH, proteins are denatured and digested, enzymes lose their ability to function, and death may occur. The principles of general acid–base equilibrium apply in the physiology of living systems.

In various animals, including humans, the acid–base homeostasis system can be analyzed into 3 subsystems that are interrelated. They are the bicarbonate buffer system, the phosphate buffer system, and the protein buffer system. Respiratory compensation and renal compensation are two ways that the body can excrete excess molecules to maintain pH. Acidosis or alkalosis results if the balance is disturbed.

The body's acid–base balance is normally tightly regulated by buffering agents, the respiratory system, and the renal system, keeping the arterial blood pH between 7.36 and 7.42. Several buffering agents that reversibly bind hydrogen ions and impede any change in pH exist. Extracellular buffers include bicarbonate and ammonia, whereas proteins and phosphate act as intracellular buffers; the relationship between multiple buffers in the same solution is described by the isohydric principle. The bicarbonate buffering system is especially key, as carbon dioxide (CO₂) can be shifted through carbonic acid (H
2CO
3) to hydrogen ions and bicarbonate (HCO−
3) as shown below.

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