How Breathing Occurs In Humans

Breathing is a process in which fresh air containing more oxygen is pumped into the lungs and the air with more carbon dioxide is pumped out of the 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 air with low oxygen and high carbon dioxide content moves out of the lungs. During rest breathing occurs rhythmically at the frequency of 15 to 20 times per minute in humans. to understand the mechanism of breathing we should keep in mind following aspects related to lungs and associated structure.

1. Lungs are spongy in nature. The lungs themselves neither pull air in and nor can they push it out. During inspiration passive expansion of elastic lungs occurs and expiration is due to a passive contraction of lungs.
2. Walls of the chest cavity are composed of ribs and intercostal 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 in two ways. Firstly, the muscles of ribs contract and elevate the ribs upward and forward, at the same time diaphragm becomes less dome like which increases space inside chest and reduces pressure due to which air rushes into lungs. This is called inspiration.

• EXPIRATION

During expiration the muscles of ribs move downward and inward. In this way from the sides of chest cavity the space becomes less. At the same time the muscles of diaphragm also relax becoming more domelike and the chest cavity is also reduce from floor. This reduction in space of the chest cavity exerts pressure on the lungs. When lungs are pressed the air inside lungs moves out of the lungs and this is expiration.