Question

What are the major transport mechanisms for CO₂? Explain.

Answer 1

CO₂ is carried by haemoglobin as carbamino haemoglobin. This binding is related to the partial pressure of CO₂. When PO₂ is low as in the tissues and PCO₂ is high, more carbon dioxide binding occurs whereas when PCO₂ is low and PO₂ is high as in the alveoli, dissociation of CO₂ from carbamino haemoglobin takes place. RBC contains a high concentration of enzyme carbonic anhydrase that converts carbon dioxide to bicarbonates and vice versa.

CO₂ diffuses the blood and forms bicarbonate ions. Thus CO₂ is trapped as bicarbonate at the tissue level and transported to the alveoli and released out as CO₂. A small amount of CO₂ dissolves in the plasma water and forms acid. On reaching the lungs carbonic acid dissociates and releases carbon dioxide. So carbon dioxide is transported as carbamino-haemoglobin, bicarbonates and carbonic acid.