Carbon dioxide production occurs in the tissues as a byproduct
of normal metabolism.
It then dissolves in the plasma and then into the red blood
cells.
Carbonic anhydrase in the RBCs catalyzes its hydration to
carbonic acid (H2CO3). Carbonic acid then spontaneously dissociates
to form bicarbonate ions (HCO3−) and a hydrogen ion (H+).
A decrease in intracellular pCO2 leads to more CO2 passively
diffusing into the cell.
RBCs exchange bicarbonate for chloride using the anion
exchanger protein. Hence, the rise in intracellular bicarbonate
leads to bicarbonate export and chloride intake. This is called a
chloride exchange.