Chloride Shift — FRCA Primary MCQ
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Correct answer: A — Chloride moves into red blood cells as bicarbonate moves out in the tissues
In the tissues CO2 enters RBCs and is converted to H2CO3 by carbonic anhydrase then dissociates to H+ and HCO3-. HCO3- is transported out of the RBC via the band 3 protein (anion exchanger) in exchange for Cl- moving in (chloride shift). This maintains electrical neutrality. The process reverses in the lungs. RBC swelling occurs in venous blood due to increased intracellular osmolality.
Reference: Power Kam 2018 Principles of Physiology for the Anaesthetist