Question

The movement of gases across the respiratory membrane depends on two major things:

• A. Membrane thickness
• B. Amount of haemoglobin
• C. Rate of diffusion of each gas
• D. Form in which each gas is transported in the blood

Answer 1

Answer: (C), (D)

Form in which each gas is transported in the blood

The movement of gases across the respiratory membrane depends on two things:

• The form in which each gas is transported in the blood: Only 2% of oxygen is transported dissolved in the plasma of blood. The rest of the oxygen, i.e 98% is carried by haemoglobin molecules in the RBCs. Carbon dioxide on the other hand is primarily transported in the plasma as bicarbonate in fact 60% is carried as ${{\mathrm{HCO}}_3}^{-}$. About 30% is transported bound to haemoglobin or bound to plasma proteins or dissolved in plasma and 10% as dissolved in blood plasma.
• The rate of diffusion of each gas: Gas exchange at both the pulmonary capillary and tissue capillary level involves simple passive diffusion of oxygen and carbon dioxide down the partial pressure gradient. No Active transport mechanism exists for these gases.