Question

Carbon dioxide (C0₂) diffuses into blood from tissue site and passes to alveolar site in the form of

• A. bicarbonate; 70%
• B. bicarbonate; 20 - 25%
• C. carbaminohaemoglobin; 60 - 70%
• D. carbaminohaemoglobin; 7%

Answer 1

Answer: (A)

Blood is the medium of transport of O₂ and CO₂. Nearly 20-25% of CO₂ is transported by RBCs as carbaminohaemoglobin whereas 70% of it is carried as bicarbonate through plasma. About 7% of CO₂ is carried in dissolved state through plasma. The largest fraction of CO₂ is converted to bicarbonate ions (HCO^-₃) and transported in plasma. When CO₂ diffuses into the RBCs, it combines with H₂O, forming carbonic acid (H₂CO₃). H₂CO₃ is unstable and quickly dissociates into hydrogen ions and bicarbonate ions.