How does breathing help buffer the pH of blood?

The carbon dioxide-bicarbonate system is the most important of the body’s buffer systems (others include intracellular proteins, hemoglobin, plasma proteins, and constituents of bone). The bicarbonate buffer system modulates pH in both intra- and extra-cellular body fluids.

Bicarbonate, present in most body fluids, constitutes a large reservoir of buffer called the alkali reserve. Bicarbonate reacts with the hydrogen ion to form carbonic acid, which exists in equilibrium with carbon dioxide.

With hydrogen ion ingestion or production by metabolizing tissues, bicarbonate converts it to carbonic acid and, ultimately, to carbon dioxide and water. And the carbon dioxide is eliminated by the lungs.

The system pH in which these reactions take place is calculated using the Henderson-Hasselbalch equation.

However, from a clinical perspective, using blood gas analysis, it makes more sense to express the concentration of H₂CO₃ as the partial pressure of CO₂ times the solubility factor for CO₂.

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