What is the role of surfactant in the alveoli?

 # What is the role of surfactant in the alveoli?

 A. To increase the surface tension of alveolar fluid

 B. To transport oxygen across the alveolar membrane

 C. To warm the inspired air

 D. To reduce the surface tension of alveolar fluid

The correct answer is D. To reduce the surface tension of alveolar fluid.

Surfactant, produced by type II alveolar cells in the lungs, is a lipoprotein mixture that reduces the surface tension of the fluid lining the alveoli. By lowering surface tension, surfactant prevents the alveoli from collapsing during exhalation, stabilizes alveolar size, and reduces the work of breathing by making it easier for the lungs to expand during inhalation.

• A. To increase the surface tension of alveolar fluid: Incorrect, as surfactant decreases, not increases, surface tension.
• B. To transport oxygen across the alveolar membrane: Incorrect, as oxygen diffusion occurs passively across the alveolar membrane and is not facilitated by surfactant.
• C. To warm the inspired air: Incorrect, as warming inspired air occurs primarily in the upper respiratory tract, not the alveoli, and is unrelated to surfactant function.