Q.7 Describe the mechanism of breathing
The physical movements associated with the gaseous exchange are called breathing.
Phases of Breathing
There are two phases of breathing i.e.
1. Inhalation or inspiration
a) Contraction of rib muscles and diaphragm
During inspiration the rib muscles contract and ribs are raised. At the same time the dome shaped diaphragm contracts and is lowered.
b) Effect of contraction
These movements increase the area of the thoracic cavity which reduces the pressure on lungs. As a result, the lungs expand and the air pressure within them also decreases. The air from outside rushes into the lungs to equalize the pressure on both sides.
2. Exhalation or expiration
a) Relaxation of rib muscles and diaphragm
After the gaseous exchange in the lungs, the impure air is expelled out in exhalation. The rib muscles relax bringing the ribs back to the original position. The diaphragm muscles also relax and it
gets its raised dome shape.
b) Effect of relaxation
This reduces the space in the chest cavity and increases the pressure on lungs. The lungs contract and the air is expelled out of them.