Which of the Following is Necessary for the Lungs to Remain

Question

Which of the following is necessary for the lungs to remain expanded?
A) The alveolar cells must secrete surfactant.
B) The intrapulmonic pressure must be negative.
C) The glottis must be closed.
D) The intrapleural pressure must be negative.

Accepted Answer

The negative intrapleural pressure is necessary to keep the lungs expanded. It creates a suction force that keeps the lungs against the chest wall. Choice A is incorrect because surfactant is necessary to reduce surface tension and prevent the collapse of alveoli, but not necessary to keep the lungs expanded. Choice B is incorrect because a negative intrapulmonic pressure is not necessary to keep the lungs expanded; it is necessary for air to enter the lungs during inspiration. Choice C is incorrect because the glottis is not involved in the process of keeping the lungs expanded.