Question

During expiration the diaphragm becomes
A. Oblique
B. Dome- shaped
C. Flattened
D. Normal

Answer 1

Hint:- The process of breathing consists of two steps. They are inspiration or inhalation and expiration or exhalation. Inspiration is an active process in which atmospheric air is taken into the lungs. Expiration is a passive process in which the air from lungs is expelled out into the atmosphere. The intake of air into the lungs and expulsion of air from the lungs is carried out by creating a pressure gradient between lungs and the atmosphere.

Complete answer:
Diaphragm is the primary inspiratory muscle. In the process of breathing, an inspiration is followed by an expiration. The muscles contracted during inspiration become relaxed during expiration. In the relaxed state, the diaphragm attains a dome-shape which occurs during expiration.
Inspiration is an active process which is initiated by the contraction of diaphragm and the external intercostal muscles. During contraction, the diaphragm flattens thereby, increasing the volume of thoracic cavity anterior- posteriorly. The contraction of the external intercostal muscles lifts up the ribs and sternum, increasing the volume of the thoracic cavity. As the volume of thoracic cavity increases, volume of the intrapulmonary cavity increases and the intrapulmonary pressure decreases than the atmospheric pressure. Thus, inspiration occurs.
Expiration or exhalation is a passive process which involves the relaxation of diaphragm and external intercostal muscles which returns the diaphragm, sternum and ribs into their normal position thereby reducing the volume of the thoracic cavity. The decrease in the volume of thoracic cavity decreases the intrapulmonary volume and increases the intrapulmonary pressure than the atmospheric pressure. Thus, expiration is caused.
Thus, the right option is B.

Note:- An inspiration is followed by an expiration and this cycle is called a respiratory cycle. The number of cycles per minute is known as the respiratory rate. Normally, a man breathes 15 to 20 times a minute. The volume of air involved in breathing can be estimated using an instrument called a spirometer. Apart from the diaphragm and intercostal muscles, the abdomen muscles can also help to increase the strength of breathing.