Gas Transport
After O2 is diffused through the respiratory membrane, it enters and dissolves into the blood plasma.
Over 98% of the O2 carried in the blood is bound to hemoglobin (which becomes oxyhemoglobin). As long as the PO2 remains relatively high, O2 will remain attached to the hemoglobin. As PO2 decreases, the O2 – hemoglobin bone weakens and eventually, the O2 will release and go into the nearby tissues.
- O2 release is also affected by PC02, blood pH and blood temperature.
CO2 is transported as a molecule dissolved in the plasma (7%), as part of carbaminohemoglobin (23%) or as bicarbonate ions (70%).
- CO2 will react with water (plasma) to form carbonic acid, and subsequently bicarbonate ion, but slowly. Carbonic anhydrase catalyzes this reaction, then the free H+ is picked up by hemoglobin.
The low PC02 in the alveoli causes CO2 to come out of solution (if it was dissolved in the plasma), to release from hemoglobin’s NH2 site and/or to reform from the bicarbonate ion and H+ (this last under the influence of carbonic anhydrase again)