Question

Follow an O₂ molecule from an alveolus to a body cell. This process should include detailed descriptions of diffusion and gas transport.

Answer 1

Answer.

The oxygen transported from the atmosphere to body tissues through the lungs and blood by diffusion process.

Diffusion process:

Alveoli are the primary sites of exchange of gases in the lungs. Exchange of gases also occur between the blood and tissue. O2 and CO2 are exchanged in these sites by simple diffusion. The exchange of gases is based on some important factors that can affect the rate of diffusion. These are 1) partial pressure 2) solubility of the gases 3) thickness of respiratory membrane, 4) surface area, 5) distance of diffusion.

The pressure contributed by an individual gas in a mixture of gases is called partial pressure.

As the solubility of CO2 in 20-25 times higher than that of O2 the amount of CO2 that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of O2.

Pulmonary gas exchange:

Difference in pO2 and pCO2 of alveolar air and pulmonary capillaries favour the diffusion of O2 from the alveolar air into the blood in the pulmonary capillaries and diffusion of CO2 in the opposite direction.

Transport of oxygen:

Oxygen is transported from lungs to the tissue through the plasma and RBC of blood. 100ml of oxygenated blood can delover 5ml of O2 to the tissue under normal conditions.

1) Transport of oxygen through the plasma :

About 3℅ of O2 is carried through the blood plasma in a dissolved state.

2) Transport of oxygen by red blood cells:

About 97℅ of O2 is transported by the RBCs in the blood. Haemoglobin is a red coloured iron containing pigment present in RBCs. Each haemoglobin molecule can carry a maximum of four molecules of oxygen. Binding of oxygen with haemoglobin is primarily related to partial pressure of O2. At lungs, where the partial pressure of O2 ( oxygen tension) Is high. Oxygen binds to haemoglobin (purplish- bluish- red in colour) in reversible manner to from oxyhaemoglobin ( bright red in colour) this is called oxygenation of haemoglobin.

At the tissue, where the partial pressure of O2 is low, oxyhaemoglobin dissociate into haemoglobin and oxygen. The other factors that influence binding of oxygen with haemoglobin are the partial pressure of CO2, the hydrogen ion concentration (pH) and temperature.