Question

Define breathing and explain the mechanism of breathing in human beings.

Answer 1

Breathing:

1. The process in which air moves in and out of the lungs is known as breathing.
2. The breathing mechanism involves two processes:
   1. Inspiration
   2. Expiration

Mechanism of Inspiration

1. The process of intake of the atmospheric air is called inspiration.
2. It is an active process.
3. When the volume of the thoracic cavity increases & the air pressure decreases, inspiration takes place.
4. Contraction of the external intercostal muscles increases the volume of the thoracic cavity.
5. Contraction of the diaphragm also further increases the size of the thoracic activity.
6. Simultaneously, the lungs expand.
7. With this expansion of the lungs, the air pressure inside the lungs decreases.
8. The pressure equalizes & the atmospheric air rushes inside the lungs.

Mechanism of Expiration

1. The process of exhaling CO₂ is called expiration.
2. It is a passive process.
3. It seems to occur when the size of the thoracic activity decreases and the air pressure outside increases.
4. Now, the external intercostal muscles relax & the internal intercostal muscles contract.
5. As a result, the ribs are pulled inwards & the size of the thoracic cavity is reduced.
6. The diaphragm is normally relaxed and the lungs get compressed.
7. Consequently, the pressure increases, and the air is forced outside.