When the diaphragm contracts
A) the volume of the thoracic cavity increases.
B) lung volume increases as the lungs are forced to expand.
C) the intra-alveolar pressure increases.
D) both (a) and (b) above.
E) all of these answers.

Question

Quizplus · Accepted Answer

When the diaphragm contracts, it moves downward, which increases the volume of the thoracic cavity (choice A) and creates negative pressure within the pleural cavity. This negative pressure helps to expand the lungs (choice B) and draw in air. The intra-alveolar pressure decreases as a result of this expansion, allowing air to flow into the lungs. Therefore, both choices A and B are correct. Choice C is incorrect because the contraction of the diaphragm creates negative, not positive, pressure within the alveoli. Therefore, the correct answer is D.

When the Diaphragm Contracts