A buffer system in the human body is an interaction between a weak acid-base conjugate pair that keeps the body at the proper pH. A conjugate acid-base pair is typically composed of a weak acid and the basic ion formed when that acid loses a hydrogen ion. Weak acids tend to be organic, such as carbonic acid or acetic acid.
The circulatory system cleans up the acid and carbon dioxide produced by exercise by taking it into the blood. This could result in a dangerous condition called acidosis, but the bicarbonate buffer system maintains the blood pH at 7.4. The bicarbonate buffer system works by donating protons if the substances carried in the blood stream are too basic and accepting protons if the substances are too acidic. In the example above, when the blood becomes more acidic due to exercise, the additional protons from those acids are absorbed by the bicarbonate in the blood to form carbonic acid. The increase in carbonic acid in the blood stimulates the lungs to expel more CO2, which eventually causes the acid in the blood to be lowered back to a normal range.
