Question

Explain what takes place during the Chloride Shift at the pulmonary capillaries of the lungs and why this is important.

Answer 1

Chloride shift or Hamburger phenomenon is the ex- change of a chloride ion for a bicarbonate ion across RBC membrane. It was discovered by Hartog Jakob Hamburger in 1892.
Chloride shift occurs when carbon dioxide enters the blood from tissues. In plasma, plenty of sodium chloride is present. It dissociates into sodium and chloride ions. When the negatively charged bicarbonate ions move out of RBC into the plasma, the negatively charged chloride ions move into the RBC in order to maintain the electrolyte equilibrium (ionic balance).
Anion exchanger 1 (band 3 protein), which acts like antiport pump in RBC membrane is responsible for the exchange of bicarbonate ions and chloride ions. Bicarbonate ions combine with sodium ions in the plasma and form sodium bicarbonate. In this form, it is transported in the blood.
Hydrogen ions dissociated from carbonic acid are buffered by hemoglobin inside the cell.
Reverse Chloride Shift
Reverse chloride shift is the process by which chloride ions are moved back into plasma from RBC shift. It occurs in lungs. It helps in elimination of carbon dioxide from the blood. Bicarbonate is converted back into carbon dioxide, which has to be expelled out. It takes place by the following mechanism:
When blood reaches the alveoli, sodium bicarbo- nate in plasma dissociates into sodium and bicarbonate ions. Bicarbonate ion moves into the RBC. It makes chloride ion to move out of the RBC into the plasma, where it combines with sodium and forms sodium chloride.
Bicarbonate ion inside the RBC combines with hydrogen ion forms carbonic acid, which dissociates into water and carbon dioxide. Carbon dioxide is then expelled out.