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Mechanism of Breathing

       The process of respiration takes place in two phases:

    1. Inspiration and
    2. Expiration

1. Inspiration

       Inspiration may be defined as the process of drawing in air into the lungs. It occurs with the help of diaphragm muscles. The muscles of diaphragm contract due to which diaphragm moves in the downward direction. Due to this, the volume of chest cavity increases and it results in decrease of air pressure inside the chest cavity. Now, the oxygenated air present outside the body being at high pressure flow rapidly into the lungs by passing through nasal cavity, pharynx, larynx, trachea, bronchi and bronchioles.

Inspiration and Expiration Mechanism of Breathing

Exchange of Gases

       In the lungs, oxygenated air finally reaches the tiny air sacs (alveoli) by passing through bronchioles. Now, each alveoli is thin walled and surrounded by a network of very fine blood capillaries. The oxygen gas present in the air passes through the walls of the alveoli into the blood present in blood capillaries. This blood is returned to the heart to be supplied to all the tissues of the body. In the tissues oxygen is used for oxidation of food and is converted into carbon dioxide. From the tissues, carbon dioxide is absorbed by blood and carried to the alveoli of lungs for expiration.

2. Expiration

       Expiration may be defined as the process of expelling out foul air from lungs. This happens when the muscles of diaphragm relax and come back to their original position. This decreases the volume of chest cavity, due to which our chest cavity contracts and pushes out carbon dioxide containing foul air through bronchi, trachea, larynx, pharynx, nasal cavity and nostrils.

Test Your Understanding and Answer These Questions:

  1. Give differences between inspiration and expiration.

  2. Describe the mechanism of breathing in human beings.

  3. Explain exchange of respiratory gases in lungs of human beings.

  4. What happens to the carbon dioxide which collects in human tissues?

  5. Explain the mechanism of gaseous exchange between tissues and blood.

  6. What is the normal rate of breathing in human beings under normal conditions?