Question

State the volume of air remaining in the lung after a normal breathing.

Answer 1

Hint: Breathing is characteristic of life. It is necessary because all the living cells of the body need energy which is derived from the biochemical reactions which take place in the presence of oxygen.

Complete answer:
1.Breathing is the process of moving air into and out of the lungs. The respiratory system allows the exchange of respiratory gases between the environment and the blood and the cardiovascular system transports them between lungs and the cells of the body.
The cycle of breathing consists of three phases: (i) inspiration (inhalation) (ii) expiration (exhalation) and (iii) pause.

Inspiration: It is an active process involving the contraction of one or more muscles. The contraction of the diaphragm increases the volume of the thoracic cavity. It is responsible for roughly 75 percent of air movement in normal breathing at rest. The external intercostal muscles assist in inspiration by elevating the ribs. This action contributes roughly 25 per cent to the volume of air in the lungs.

Expiration: It is either passive or active, depending on the level of respiratory activity. Normally the relaxation of diaphragm and external intercostal muscles results in expiration. When expiration is active, it may involve one or more of the internal intercostal and transverse thoracic muscles or the abdominal muscles.
3. Spirometry is the process by which volumes of air that moves into and out of the respiratory system is measured.

Volume of the air remaining in the lung after a normal breathing is FRC i.e. functional residual capacity. It is the sum of residual volume and expiratory reserve volume( 1200+1200= 2400 mL at rest).

In its residual volume (RV) is the volume of air that remains in the lungs after the most forceful expiration (1200 mL in males, 1100 mL in females). It mostly occurs in alveoli and cannot be directly measured.
And the Expiratory volume (ERV): The amount of air we can expire over and above the tidal volume by most forceful expiration (1200 mL).

The Volume of the air remaining in the lung after a normal breathing is called FRC i.e. functional residual capacity(1200+1200= 2400mL at rest)

Note: The device commonly used to measure the pulmonary volumes is a spirometer or respirometer. The recording of breathing is termed as spirogram. There are four pulmonary volumes and Five pulmonary capacities.