Question

How can pressure inside the lungs become positive for exhalation without muscle action when it usually remains negative?

a) Lung elasticity changes.
b) Diaphragm contracts.
c) Rib cage expands.
d) Air is forced out.

Answer 1

During exhalation, the pressure inside the lungs can become positive without muscle action due to surface tension in the alveoli creating a positive pressure. Muscle action can enhance this positive pressure to produce forced exhalation.

Step-by-step explanation:

Lung pressure is controlled by several mechanisms. Muscle action in the diaphragm and rib cage is necessary for inhalation; this muscle action increases the volume of the lungs thereby reducing the pressure within them. Surface tension in the alveoli creates a positive pressure opposing inhalation. You can exhale without muscle action by letting surface tension in the alveoli create its own positive pressure. Muscle action can add to this positive pressure to produce forced exhalation.