In the kidneys, the main role in acid-base homeostasis is to reclaim (reabsorb) HCO3- from the glomerular filtrate (in the proximal tubules):
- If the blood pH is decreased, HCO3- (base) is reabsorbed into the blood (with sodium) to buffer the blood.
- If the blood pH is increased, HCO3- (base) will not be absorbed; it will be eliminated in the urine.
- The kidneys can also excrete the excess acid (H+) normally produced by the body daily via the phosphate buffering system.
