When does the chloride shift occur?

What is Chloride Shift?

The chloride shift is defined as

The movement of chloride ions from the plasma into RBCs as the blood undergoes the transition from arterial to venous gas.

The chloride shift is also known as Hamburger shift. It is the process which takes place in a cardiovascular system where the exchange of bicarbonate $HCO_{3}^{-}$ and chloride Cl across the membrane of RBCs.

Following are the times when does the chloride shift occur:

• When the chloride moves into erythrocytes and bicarbonate moves out into the venous blood.
• When chloride moves out and bicarbonate moves into the pulmonary capillaries.

Mechanism behind Chloride Shift

The byproduct of normal metabolism is carbon dioxide. This byproduct dissolves in the blood plasma and in RBC where carbonic acid is formed due to hydration of carbonic anhydrase. By the Band 3 exchange protein, bicarbonate is pumped out of the RBC and chloride is pumped into it. This mechanism takes place during the circulating time.

The reverse mechanism takes place in the pulmonary capillaries. Bicarbonate is pumped back into the RBC and chloride is pumped out of RBC. Also, carbonic anhydrase converts bicarbonate into carbon dioxode and water.

Significance of Chloride Shift

Following are the significance of the chloride shift:

• The CO2 carrying capacity of venous blood increases because of the chloride shift.
• The unloading capacity of oxygen increases as there is a modulation in the hemoglobin tetramer.
• The change in pH is reduced that is caused due to metabolic byproducts.