Gas Exchange - Diffusion

Diffusion

Blood carries oxygen, carbon dioxide, and hydrogen ions between tissues and the lungs. The majority of CO₂ transported in the blood is dissolved in plasma (primarily as dissolved bicarbonate; 60%). A smaller fraction is transported in red blood cells combined with the globin portion of hemoglobin as carbaminohaemoglobin. This is the chemical portion of the red blood cell that aids in the transport of oxygen and nutrients around the body, but, this time, it is carbon dioxide that is transported back to the lung.

As CO₂ diffuses into the blood stream, it is absorbed by red blood cells before the majority is converted into H₂CO₃ by carbonic anhydrase, an enzyme that is not present in the plasma. The H₂CO₃ dissociates into H+ and HCO−
3. The HCO−
3 moves out of the red blood cells in exchange for Cl− (chloride shift). The hydrogen ions are removed by buffers in the blood (Hb).