What is the primary physiological function of pulmonary surfactant in human alveoli?
Answer and explanation
Correct answer: C. Reduces surface tension to prevent alveolar collapse during expiration
- Step 1: Alveoli are lined with a thin fluid film exhibiting high surface tension that tends to collapse small alveoli (Laplace law P = 2T/r). Step 2. Type II alveolar cells secrete surfactant (dipalmitoylphosphatidylcholine) that dramatically lowers surface tension, stabilizing alveoli. Answer: Reduces surface tension to prevent alveolar collapse during expiration. Why not the others: Increasing surface tension would cause fatal atelectasis; surfactant is not an antiviral toxin; pleural fluid lubricates pleural membranes.
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