Describe the different means by which carbon dioxide is transported in the blood

Answer 1

The CO2 is transported from the tissue to the alveoli in the blood in three ways: as a bicarbonate ion (HCO3), as carbaminohemoglobin, and dissolved in plasma. Some of the CO2 dissolves in the plasma (10 percent) and another 20 percent combines with the Hb to form carbaminohemoglobin. However, the major (70 percent) transport mechanism for carrying CO2 in the blood is the HCO3 . The increase in PCO2 in the venous blood because of diffusion from the tissues causes HCO3 to combine with water to form carbonic acid (H2CO3). This combination, or reaction, is catalyzed by carbonic anhydrase within the RBC. H2CO3 is a weak acid and easily disassociates into a hydrogen ion and a bicarbonate ion. The hydrogen ion binds to the Hb, and the bicarbonate ion diffuses out of the RBC. The bicarbonate ion is negatively charged and results in an electrochemical imbalance across the cell membrane. A chloride ion enters the RBC in a one-to-one exchange with the bicarbonate ion to keep the cell membrane electrochemically balanced, or neutral. This shift in ions is known as the chloride shift. When the blood reaches the alveoli of the lung, a reverse chloride shift occurs, in that a bicarbonate ion enters the RBC in exchange for the chloride ion, which then combines with a hydrogen ion and is released from the reduced Hb. The CO2 dissolved in the plasma diffuses across the respiratory membrane into the alveoli. The carbaminohemoglobin in the RBC releases its CO2 as oxygen combines with Hb, and it also diffuses across the respiratory membrane into the alveoli.