MECHANISM AND EVENTS OCCURRING DURING BREATHING

Events occurring during inspiration and expiration

Breathing is a process in which fresh air containing more oxygen is pumped into the lungs and air with more carbon dioxide is pumped out of lungs.

In other words, breathing is a mechanical process consisting of two phases, inspiration and expiration. During inspiration, fresh air moves in and in expiration the air with low oxygen and high concentration of Carbon dioxide moves out of the lungs. During rest breathing occurs rhythmically at the frequency of 15 – 20 times per minute in human beings.

Mechanism of Breathing:

To understand the mechanism of breathing, first you have to understand the associated parts of the lungs.

Spongy lungs:

Lungs are spongy in nature. The lungs themselves neither pull air in nor can they push it out. Diffusion of oxygen in and carbon dioxide out occurs because of difference of partial pressure of these gases. During inspiration passive expansion of elastic lungs occurs while there is passive contraction of lungs during expiration.

Diaphragm:

The floor of the chest cavity is diaphragm, which is a muscular sheet. The shape of the diaphragm is more domelike when its muscles are relaxed. On the other hand when the muscles of the diaphragm contract its shape becomes less domelike.

Ribs and muscles:

Walls of the chest cavity are composed of ribs and inter-coastal muscles. When muscles between the ribs contract, the ribs are elevated and when muscles between ribs are relaxed the ribs settle down.

Inspiration:

During inspiration the space inside the chest cavity is increased by following two ways:

• The muscles of ribs contract and elevate the ribs upwards and forwards.
• The muscles of diaphragm contract and diaphragm become less domelike.

As the result of this downward movement of diaphragm and outward and upward movement of the ribs, the pressure from the lungs is released. When the pressure from the lungs is removed they expand. With the expansion of the lungs, vacuum (low pressure area) is created inside the lungs by which the air rushes into the lungs from the onside due to higher atmospheric pressure. This is Inspiration.

Expiration:

Actually, the opposite phenomenon of inspiration is expiration. During expiration, the impure air is expelled out of the body. During expiration, the muscles of ribs become relaxed bringing the ribs back to its original position. When the ribs settle down they move downward and inward. In the mean time, the diaphragm muscles also relax getting it into more domelike shape. In this way the space in the chest cavity reduces and increases the pressure on lungs. The lungs are pressed and the inside air moves out.

Following image makes your idea clear: