Question
How does exchange of gases take place in the lungs of man?
Solution
The gaseous exchange takes place in the alveoli. Each alveolus is surrounded by a network of blood capillaries. Both alveoli and blood capillaries have a very thin single epithelial layer.
The blood contained in the capillaries of the lungs flows from the heart to the lungs. It contains very little oxygen and much of carbon dioxide. On the other hand air flowing into the alveoli contains much of oxygen (21%) and very little of CO2 (0.03%). Therefore, a two way diffusion takes place i.e., oxygen diffuses into the blood from alveoli and CO2 flows out from the blood into the alveoli. This gaseous exchange occurs within few seconds because of an extensive surface area provided by the alveoli in the lungs.
Gaseous exchange in the lungs
