Question

Describe the mechanism of respiration in man.

Answer 1

Hint: Breathing involves two main processes: inspiration and expiration. When the diaphragm and the external intercostal muscles contract, it is called inspiration. Expiration occurs when the diaphragm and the intercostal muscles relax. With the help of lungs in the body, gases are exchanged between the blood and the air.

Complete answer:
Mechanism of respiration:
- Air is drawn into the body through the nostrils.
- The air from the nasal cavity passes to the pharynx, which leads to the trachea, through a slit called the glottis.
- The trachea runs down the neck and divides into two bronchi, which lead into the lungs and further divide into smaller bronchioles. The smallest bronchioles terminate into alveoli.
- The walls of the alveoli are thin and covered by blood capillaries to facilitate the exchange of gases in the lungs.
- In the alveoli, the exchange of gases takes place, $C{O_2}$ from the blood is replaced with ${O_2}$, and$C{O_2}$ is removed out of the body.
- In humans, for the process of respiration, the air is drawn into the lungs by the process of breathing.

Additional information:
The mechanism of respiration involves five steps: -
> Breathing or pulmonary ventilation: It involves both inhalations in which an adequate amount of oxygen is taken inside and exhalation involves the removal of carbon dioxide with air.

> External respiration: This is the exchange of oxygen to the blood and of carbon dioxide from the blood to alveoli and is done due to their concentration gradient.

> Transport of ${O_2}$ to tissue: Oxygen binds to hemoglobin and reaches to tissues.

> Internal respiration: As the concentration of oxygen is less and carbon dioxide is more in number the hemoglobin releases oxygen and is absorbed by the tissue.

> Transport of $C{O_2}$ from tissue: - The carbon dioxide released by tissue transported in the form of bicarbonate, carbamino-hemoglobin, and dissolved in the blood reaches to alveoli then diffuses from blood and released out.

Note: The air which is breathed in and out of the lungs varies in its pressure. When there is a fall in air pressure the alveolar spaces fall and the air enters the lungs (inspiration) and as the pressure of the alveoli exceeds the atmospheric pressure, the air is blown from the lungs (expiration). The flow rate of air is in proportion to the magnitude of the pressure difference.