Question

Bulk of carbon dioxide $\left(C{O}_2\right)$ released from body tissues into the blood is present as

• A. Bicarbonate in blood plasma and RBCs.
• B. Free $C{O}_2$ in blood plasma.
• C. 70% carbamino haemoglobin and 30% as bicarbonate.
• D. Carbamino haemoglobin in RBCs.

Answer 1

The correct option is A Bicarbonate in blood plasma and RBCs.

70% to 75% $C{O}_2$ is transported as $NaHC{O}_3$ by plasma and $KHC{O}_3$ by RBCs. Carbonic anhydrase (CA) within the red blood cells quickly converts the carbon dioxide into carbonic acid (H${}_2$CO${}_3$). Carbonic acid is an unstable, intermediate molecule that immediately dissociates into bicarbonate ions (HCO${}_3$) and hydrogen (H${}^{+}$) ions. Since carbon dioxide is quickly converted into bicarbonate ions, this reaction allows for the continued uptake of carbon dioxide into the blood, down its concentration gradient. It also results in the production of H${}^{+}$ ions.