Final answer:
The chloride shift exchanges chloride ions for bicarbonate ions across the erythrocyte membrane, facilitated by the enzyme carbonic anhydrase, to maintain blood pH and carbon dioxide transport.
Step-by-step explanation:
In the chloride shift, chloride ions are exchanged for bicarbonate (HCO3−) ions across the erythrocyte membrane. This process is crucial for the transport of carbon dioxide in the blood and helps maintain the acid-base balance. Inside the red blood cells, carbonic anhydrase (CA) catalyzes the conversion of carbon dioxide and water into carbonic acid, which then dissociates into hydrogen (H+) ions and bicarbonate ions. Bicarbonate tends to accumulate inside the erythrocytes, leading to a concentration gradient that facilitates its exit from the cells in exchange for chloride ions. As this exchange occurs, the electrical balance of erythrocytes and blood remains unchanged thanks to the trade of one negatively charged ion for another. The process reverses in the lungs, where bicarbonate re-enters erythrocytes and carbon dioxide is expelled.