Question

During expiration the volume of the chest cavity __________ and the intrapulmonary pressure __________.

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

Answer 1

The correct option is B decreases, increases

Expiration is a process in which air is drawn out of the lungs. During expiration, the diaphragm relaxes and returns back to its usual position. The volume of the thoracic cavity decreases in the longitudinal direction. The external intercostal muscles also relax and the chest returns to its original position by moving downwards and inwards. As the chest moves downwards and inwards, the thoracic cavity contracts in the dorsoventral direction.
Due to the contracting of the thoracic cavity the volume inside the lungs decreases. It is known from Boyle’s law that for gases constant temperature the volume is inversely proportional to the pressure. So when the volume decreases, the pressure increases and goes above the atmospheric pressure.
Therefore, during expiration the volume of the chest cavity decreases and the intrapulmonary pressure increases.