Chloride helps maintain acid-base balance by performing which of the following roles?
A. Participating in the chloride shift.
B. Following sodium to maintain serum osmolarity.
C. Maintaining the balance of cations in the ICF and ECF.
D. Separating carbonic acid.
Correct Answer: A. Participating in the chloride shift.
To maintain acid-base balance, chloride shifts into and out of red blood cells in exchange for bicarbonate. In the presence of an acid-base imbalance, chloride levels change independently of sodium. Because of its inverse relationship with bicarbonate, chloride losses result in an increase in bicarbonate, and chloride gains result in a decrease in bicarbonate.
Option B: 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.
Option C: The kidneys help maintain the acid–base balance by excreting hydrogen ions into the urine and reabsorbing bicarbonate from the urine. Acid–base homeostasis concerns the proper balance between acids and bases; it is also called body pH. The body is very sensitive to its pH level, so strong mechanisms exist to maintain it.
Option D: This reaction can and does occur without an enzyme; however, carbonic anhydrase is an enzyme that assists with this process. It catalyzes the first reaction above to form carbonic acid which can then freely dissociate into bicarbonate and a hydrogen ion. Carbonic anhydrase is located in red blood cells, renal tubules, gastric mucosa, and pancreatic cells.
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