In lungs, there is an exchange of ions between RBC and Plasma. Removal of CO2 from blood involves ______________.
Efflux of Chloride ions from RBC
Once blood reaches the lungs, CO2 must diffuse across the capillary and alveolar membrane. How does it do this if it is dissolved in plasma as bicarbonate? In the lungs, the partial pressure of CO2 is low and that of O2 is high. This has two major effects. First, hemoglobin, which has a higher affinity for oxygen, will make it diffuse into the RBCs and bind to the hemoglobin, displacing the hydrogen ions. Secondly, the CO2 concentration is lowered. This disturbs the equilibrium of the reaction catalyzed by carbonic anhydrase, and drives its reversal. There is an attempt to increase the number of CO2 molecules and decrease the number of hydrogen molecules. The Cl−HCO3 pump reverses, pumping chloride out of the RBC (Efflux), and bicarbonate back into the RBCs. This HCO3 then combines with the displaced hydrogen ions to form bicarbonate, which divides into CO2 and H2O. This reaction is once again catalyzed by carbonic anhydrase. This CO2 then diffuses across its partial pressure gradient into the alveoli.