Question

brielfy explain how the exchange of oxygen and carbon dioxide takes place at the lungs and tissues and what factor determines this?

Answer 1

At tissue level,

Haemoglobin (Hb) contains 2 alpha chain and 2 beta chains.CO2 coming out from the cells to the blood 20% is combined with plasma, The other 70% will combine with water to form Carbonic acid in presence of carbonic anhydrase, the intermediate product carbonic acid undergo dissociation to form the H+ and the HCO3- will go out of the plasma acting as a bufdering system, to counteract this mechanism, Cl- will come int the Haemoglobin.(chloride shift). When the CO2 binds the haemoglobin molecule & H+ binds on the aminoacid chain on the Hb to change the shape of the molecule causing the breakage of O2-Hb bond and goes out into the tissues.

In the tissues, since the cell respiration occurs by using the oxygen, Heat and ATP are produced.The haeme protein undergoes conformational chain whenever heat is produced in the tissue, which also causes the breakage of bond between the O2 &Hb. This is called the Bohr effect.

Hb affinity for O2 is high, But whenever CO2 /H+/TEMPERATURE is there, the sffinity to O2 decreases and to CO2 INCREASES.Thus Hb unload the O2. THESE FACTORS DETERMINE THE DISSOCIATION OF O2 at the tissue level.

In lung, The partial pressure of gases determine the binding of the Hb to O2 & CO2.