Buffering Blood pH, Worked

Buffering blood pH means a matched pair of substances absorbs excess acid or base as it forms, holding blood pH inside its narrow working range without any conscious effort.

Blood pH normally holds close to a narrow range, and the carbonic acid–bicarbonate system is the main buffer that keeps it there. Carbon dioxide from ordinary metabolism combines with water in the blood to form carbonic acid, a weak acid; carbonic acid can release a hydrogen ion and become bicarbonate, a weak base. Both forms exist together in the blood, and the reaction between them can run in either direction depending on what the blood needs. If metabolic activity adds excess hydrogen ions, bicarbonate absorbs them and shifts back toward carbonic acid, holding the pH from dropping much. If base is added instead and hydrogen ions grow scarce, carbonic acid releases hydrogen ions and shifts toward bicarbonate, holding the pH from rising much. The lungs reinforce this directly: carbonic acid can also break down into carbon dioxide and water, and exhaling that carbon dioxide pulls the whole system further toward absorbing more acid. Breathing faster during exercise helps this buffer keep pace with the acid active muscles produce.