Question

Define surface tension and relate it to alveolar filling.

A) Surface tension is the force that pulls fluid molecules inward and resists the expansion of alveoli. It plays a role in keeping alveoli from collapsing during expiration.
B) Surface tension is the force that pushes fluid molecules outward and aids in the expansion of alveoli. It assists in alveolar filling during inspiration.
C) Surface tension has no relation to alveolar filling, and it is a property of solid surfaces.
D) Surface tension is the force that opposes alveolar filling, making it more difficult for the lungs to expand during inspiration.

Answer 1

Surface tension is the force of attraction among molecules at a liquid's surface. In the lungs, it can lead to alveolar collapse, but pulmonary surfactant helps reduce this tension, aiding in alveolar stability during breathing.

Step-by-step explanation:

Surface tension is the force exerted by the attraction of molecules at the surface of a liquid, which makes the surface layer act as a stretched elastic membrane. In the context of the lungs and alveolar filling, surface tension is crucial because it influences the expansion and contraction of the alveoli, the tiny air sacs where gas exchange occurs. Without the presence of a pulmonary surfactant, surface tension would cause the alveoli to collapse upon exhalation due to the water present in the lining of the alveoli which increases this force.

However, the pulmonary surfactant secreted by type II alveolar cells reduces surface tension, thereby stabilizing the alveoli. During inhalation, the surfactant molecules are pulled apart as alveoli expand, temporarily increasing surface tension. Conversely, during exhalation, these molecules come closer together, decreasing the surface tension and helping to prevent alveolar collapse. This ensures that small alveoli don't collapse and large alveoli are not able to overexpand, a function that is not shared by ordinary detergents that only reduce surface tension.