The Chloride Shift
- The chloride shift is the movement of chloride ions into red blood cells that occurs when hydrogen carbonate ions are formed
- Hydrogen carbonate ions are formed by the following process
- Carbon dioxide diffuses into red blood cells
- The enzyme carbonic anhydrase catalyses the combining of carbon dioxide and water to form carbonic acid (H2CO3)
CO2 + H2O ⇌ H2CO3
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- Carbonic acid dissociates to form hydrogen carbonate ions and hydrogen ions
H2CO3 ⇌ HCO3- + H+
- Negatively charged hydrogencarbonate ions formed from the dissociation of carbonic acid are transported out of red blood cells via a transport protein in the membrane
- To prevent an electrical imbalance, negatively charged chloride ions are transported into the red blood cells via the same transport protein
- If this did not occur then red blood cells would become positively charged as a result of a build up of hydrogen ions formed from the dissociation of carbonic acid
Examiner Tip
Be sure to learn the differences between the Bohr shift and chloride shift. The Bohr shift occurs when a high partial pressure of carbon dioxide causes haemoglobin to release oxygen into respiring tissues, while the chloride shift refers to the movement of chloride ions into red blood cells.
