Question

Bulk of carbon dioxide $\left({\left(CO\right)}_2\right)$ secreted from body tissues into the blood is present in the form of ______.

• A. bicarbonate in blood plasma and RBCs
• B. free $C{O}_2$ in blood plasma
• C. $70\%$ carbamino-haemoglobin and $30\%$ as bicarbonate
• D. carbomino-haemoglobin in $RBCs$

Answer 1

Answer: (A)

There are 3 ways for the transport of carbon dioxide which are the following:
1. In dissolved state - Approximately 5-7% of CO₂ is transported in a dissolved state in the plasma.
2. In the form of bicarbonate - The CO₂ produced by the tissues goes passively into the blood and enters into the erythrocytes where it reacts with water to form carbonic acid (H₂CO₃). This reaction is catalysed by the enzyme present in RBCs, named as carbonic anhydrase. Immediately after the formation of carbonic acid, it dissociates into hydrogen (H⁺) and bicarbonate (HC0₃^-) ions. Nearly 70% of CO₂ is transported through the blood as bicarbonate.
3. Approximately 20-25% of CO₂ is transported by erythrocytes as carbaminohaemoglobin. The CO₂ can react with the amine group of haemoglobin to form carbaminohaemoglobin.