Final answer:
Bicarbonate usually has a renal clearance close to zero in healthy people. It is freely filtered through the glomerulus, but cannot pass freely into the renal tubular cells. Hydrogen ions combine with bicarbonate to form carbonic acid, which dissociates into CO2 gas and water.
Step-by-step explanation:
Bicarbonate usually has a renal clearance close to zero in healthy people. Bicarbonate ions are freely filtered through the glomerulus, but they cannot pass freely into the renal tubular cells and must be converted into CO2 in the filtrate. Sodium ions are reabsorbed at the membrane, and hydrogen ions are expelled into the filtrate. The hydrogen ions combine with bicarbonate, forming carbonic acid, which dissociates into CO2 gas and water. The gas diffuses into the renal cells where it is converted back into a bicarbonate ion, which enters the blood.