Question

During inspiration the volume in the lungs________________ and the intrapulmonary pressure _____________

• A. increases, increases
• B. decreases, increases,
• C. increases, decreases
• D. decreases, decreases

Answer 1

The correct option is C increases, decreases

Inspiration is a process in which air is drawn into the lungs. During inspiration, the diaphragm contracts because of which it gets pulled down and the thoracic cavity expands in the longitudinal direction. The external intercostal muscles also contract because of which the chest expands upwards and outwards. As the chest expands upwards and outwards, the thoracic cavity expands in the dorsoventral direction.
Due to the expansion of the thoracic cavity the volume inside the lungs increases. It is known from Boyle’s law that for gases at a constant temperature, the volume is inversely proportional to pressure. During inspiration, when the volume inside the lungs increases, the intrapulmonary pressure (pressure inside the lungs) decreases and falls below the amospheric pressure. Hence, air enters into the lungs.
During expiration, the volume inside the lungs decreases . Due to this the intrapulmonary pressure increases and air comes out of the lungs.