Write about the mechanism of respiration in human beings.
1) Respiration in man occurs in two stages. They are inspiration and expiration.
2) During inspiration air from outside enters into the lungs by increasing the thoracic . cavity.
3) Increase in the thoracic cavity is made by pulling the diaphragm down and pushing the ribs forward.
4) As the air pressure in the lungs is reduced, air from outside enters the lungs through external nostrils, nasal cavities, pharynx, epiglottis, larynx, trachea, bronchi and bronchioles and finally reach the alveoli where exchange of gases takes place.
5) During expiration the diaphragm and ribs come back to original positions.
6) This reduces the volume of thoracic cavity.
7) So the volume of lungs is decreased and air under pressure comes out of the lungs.