Question

Diffusion of gases occurs in the alveolar region only and not in the other parts of respiratory system. Why?

Answer 1

1. Gaseous Exchange There are about 300 million air pockets or alveoli, in the human lungs. A dense network of blood capillaries is spread in their thin wall.
2. The network of blood capillaries is not spread in the trachea, bronchi, bronchioles, alveolar tubes, etc. Their walls are thick. Therefore, except the alveoli, there is no gaseous exchange in other respiratory parts. Normally, out of 500 ml of inhaled, flowing air, about 350 ml reaches the alveoli; the rest remains in the respiratory tract.
3. The walls of the air cells and the walls of the blood capillaries together form the respiratory system. Due to this, the exchange of O₂ and akes takes place easily. Gaseous exchange occurs by simple diffusion. In this process, gases diffuse from higher partial pressure to lower partial pressure.
4. The partial pressure of O₂ in the alveoli is 100–104 mm Hg and the partial pressure of CO₂ is 40 mm Hg. The impure blood in the blood capillaries in the lungs has a partial pressure of CO₂ of 40 mm Hg and a partial pressure of CO₂ of 45- 46 mm Hg.

Oxygen diffuses from the air of the alveoli into the blood and CO₂ diffuses from the blood into the air of the alveoli. In this way, the blood becomes oxygenated in the blood capillaries, which carry blood from the air sacs. The air exhaled from the lungs contains O₂ about 15.7% and CO₂ about 3.6%.