Blood Buffer - Normal Bodily Function
Metabolic waste products are transferred from muscles and organs into the blood. As there are a number of acids produced, this would have the effect of lowering the blood pH. The buffer system counteracts this effect.
Consider the production of lactic acid in muscles. Lactic acid is a weak acid and, when it enters the blood, donates a proton to water to produce H3O+. This increases the H3O+ concentration. In order to restore the H3O+ concentration to normal, the equilibrium below shifts to the left.
H2CO3 + H2O 
H3O+ + HCO3-
This shift results in the production of H2CO3. In order to reduce the H2CO3 concentration, the equilibrium below shifts to the left as well.
2 H2O + CO2 H2CO3
This shift results in the production of CO2. In the lungs, the CO2 leaves the blood, is exhaled and normal blood pH is maintained.
Continue and read about respiratory problems that cause changes in blood pH.
