What is breathing ? Explain the mechanism.

Explanation

It is a process of intake of oxygen, and leaving out carbon dioide from the lungs. The mechanism of breathing involves.
1. Inspiration ( Inhalation) `:` It is the process of drawing air into the lungs the from outside atmosphere ( intake of air ) . During this process, muscles ofthe diaphragm contract , which increases the length of the thorax. In the meanwhile intercostal muscles also contract, pulling the ribs outward .This phenomenon incrases width of the thorax, resulting in the expansion of the lungs. As a consequence pulmonary pressure falls. So oxygen rich air rushes into the lungs and fill alveoli.
2. Exchange of gases `:` The alveoli are closely surrounded by a thin walled epithelium, having capillary network. The oxygen is under high pressure in alveoli, because of its higher concentration. Similarly carbon dioxide concentration, and pressure will be more in the capillaries containing impure blood.
So, the exchange occurs by diffusion through the capillary walls. The oxygen is drawn into the blood, and carbon dioxide is pushed into the alveoli.
3. Expiration ( exhalation ) `:` It is the process of throwing out carbon dioxide from the lungs to outside. During this process, muscles of the diaphragm and intercostal muscles relax casuing the collapse of the rib cage. This decreases the volume of the thorax and lungs. As a consequence pulmonary pressure increases. So, carbon dioxide rich air of the alveoli is drawn out thorugh the respiratory passage.