How does exchange of respiratory gases take place in the alveoli of lungs

Answer:

O₂ and CO₂ are exchanged by simple diffusion between the blood and alveolar air,

mainly based on pressure/concentration gradient.

- The thickness of the membrane and the solubility of gases are two important factors

involved in diffusion.

- The diffusion membrane is made up of three major layers:

(i) Squamous epithelium of alveoli.

(ii) Endothelium of blood vessel.

(iii) Basement membrane between between these two.

- The total thickness is about 0.2 mm.

- Partial pressure for oxygen (pO₂) of alveolar air (104 mm Hg) is higher than that of

the blood capillaries (40 mm Hg), so oxygen diffuses from the alveoli into the

blood vessels.

- Partial pressure for Carbon dioxide (pCO₂) of blood capillaries (45 mm Hg) is

higher than that of alveolar air (40 mm Hg), so carbon dioxide from the blood

capillaries diffuses into the alveoli.