Question

Read the following statements regarding the mechanism of respiration and choose the correct option.
$1$. Inspiration occurs only when there is negative pressure in the lungs with respect to the atmosphere.
$2$. Expiration takes place only when intrapulmonary pressure is lower than atmospheric pressure.
$3$. Pressure gradients are generated with the help of the diaphragm and intercostal muscles.
$4$. Inspiration is initiated by the relaxation of the diaphragm.
$5$. Contraction of the diaphragm reduces pulmonary volume and increases intrapulmonary pressure causing expiration.

• A. $1,2$ and $5$ correct
• B. $2$ only correct
• C. $2,5$ correct
• D. $1,3$ correct
• E. $1,4$ correct

Answer 1

The correct option is D $1,3$ correct

• A pressure gradient is the pressure difference between the lungs and the atmosphere generated with the help of the diaphragm and intercostal muscles.
• Inspiration involves the contraction of diaphragm and external intercostal muscles whereas expiration involves relaxation of diaphragm and contraction of internal intercostal muscles.
• In humans, inspiration is an active process. During the resting state, the diaphragm is dome-shaped. On contraction, it turns flat which increases the size of the thoracic chamber anteroposteriorly. The intrapulmonary pressure becomes negative with respect to the atmosphere and the air moves in.
• At the resting state, expiration is a passive process. It occurs due to elastic recoil of the lungs. When the intrapulmonary pressure is increased with respect to the atmosphere, and the diaphragm is relaxed the expiration took place.

Statements 1 and 3 correct. Hence the correct answer is an option (D).