Explain the transport of carbon dioxide .

Explanation

Blood transports `CO_(2)` from the tissue cells to the lungs in three ways :
(i) Dissolved in plasma : About 7-10% of `CO_2` is transported in a dissolved form in the plasma.
(ii) Bound to haemoglobin : About 20-25 % of dissolved `CO_2` is bound and carried in the RBCs as carbaminohaemoglobin `(Hb CO_(2)`)
`CO_(2) + Hb to Hb CO_(2)`
(iii) As bicarbonate ions in plasma about 70% of `CO_(2)` is transported as bicarbonate ions . This is influenced by `pCO_(2)` and 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 .
`to` At the tissues the `pCO_(2)` is high due to catabolism and diffuses into the blood to form `HCO_(3)^(-)` and `H^(+)` ions . When `CO_2` diffuses into the RBCs , it combines with water forming dissociates into hydrogen and bicarbonate ions .
Carbonic anhydrase facilitates the reaction in both directions.
`CO_(2) + H_(2) O underset("carbonic anhydrase") (to) H_(2) CO_3 underset("carbonic anhydrase") (larr) HCO_(3)^(-) + H^(+)`
The `HCO_(3)^(-)` moves quickly from the RBCs into the plasma , where it is carried to the lungs . At the alveolar site where `pCO_(2)` is low , the reaction is reversed leading to the formation of `CO_(2)` and water . Thus `CO_(2)` trapped as `HCO_(3)^(-)` at the tissue level is transported to the alveoli and released out as `CO_(2)` . Every 100 mL of deoxygenated blood delivers 4 mL of `CO_(2)` to the alveoli for elimination .