ABSTRACT
As the main extracellular buffering system, carbon dioxide and bicarbonate play a crucial role in acid–base balance. The kidneys have an important role in adjusting plasma bicarbonate concentration. Bicarbonate is freely filtered in the renal corpuscle, and most is normally reabsorbed by the renal tubules. To correct an alkalosis, the kidneys reabsorb less bicarbonate and reduce the plasma bicarbonate concentration. In the kidney, the excretion of a hydrogen ion in the urine is equivalent to the addition of a bicarbonate ion to blood. Similarly, the loss of a bicarbonate ion in the urine is equivalent to the addition of a hydrogen ion to blood. The catabolism of protein and oxidation of the constituent amino acids by the liver produces some glutamine. The proximal tubular cells take up glutamine and metabolize it to ammonium ions. Renal tubular cell glutamine metabolism and ammonium ion secretion are governed by the extracellular hydrogen ion concentration, stimulated by acidosis and inhibited by alkalosis.
