Explain transport of carbon dioxide ( class 11 )

1.	Explain transport of carbon dioxide ( class 11 )
Answer» Blood transports CO2\xa0from the tissue cells to the lungs in three ways:1. Dissolved in plasma :\xa0About 7 – 10% of CO2\xa0is transported in a dissolved form in the plasma.2. Bound to haemoglobin :\xa0About 20 – 25% of dissolved CO is bound and carried in the RBCs as carbaminohaemoglobin (Hb CO2\xa0) CO2\xa0+ Hb → Hb CO2\xa0.3. As bicarbonate ions in plasma about 70% of CO2\xa0is transported as bicarbonate ions. This is influenced by pC02\xa0and the degree of haemoglobin oxygenation. RBCs contain a high concentration of the enzyme, carbonic anhydrase, whereas small amounts of carbonic anhydrase is present in the plasma.→ At the tissues the pCO2\xa0is high due to catabolism and diffuses into the blood to form HCO2\xa0and H ions. When CO2\xa0diffuses into the RBCs, it combines with water forming carbonic acid (H2\xa0CO2\xa0) catalyzed by carbonic anhydrase. Carbonic\xa0acid is unstable and dissociates into hydrogen and bicarbonate ions.Carbonic anhydrase facilitates the reaction in both directions.The HCO3-\xa0moves quickly from the RBCs into the plasma, where it is carried to the lungs. At the alveolar site where pCO2\xa0is low, the reaction is reversed leading to the formation of CO2\xa0and water. Thus CO2\xa0trapped as HCO3-\xa0at the tissue level is transported to the alveoli and released out as CO2\xa0. Every 100 mL of deoxygenated blood delivers 4 mL of CO2\xa0to the alveoli for elimination.

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