The role of alveolar surfactant is to
[ Select ]
increase
decrease
the alveolar surface tension and to
[ Select ]
increase
decrease
alveolar compliance.

Question

The role of alveolar surfactant is to 
[ Select ]
increase
decrease
 the alveolar surface tension and to 
[ Select ]
increase
decrease
 alveolar compliance.

BlackTom AI · Accepted Answer

Alveolar surfactant reduces surface tension at the air–liquid interface of the alveoli, so it decreases alveolar surface tension and thereby increases alveolar compliance.

1) Relevant concepts:
- Surface tension: cohesive forces at the liquid lining of alveoli that tend to collapse them inward. Higher surface tension increases the pressure tending to collapse a spherical alveolus.
- Law of Laplace for a sphere: P = 2T / r, where P is the pressure needed to keep the alveolus open, T is surface tension, and r is radius.
- Compliance: C = ΔV / ΔP — the lung’s volume change per unit pressure change. Lower pressure required to expand the lung (smaller P) yields greater compliance.

2) Step-by-step reasoning:
- Surfactant molecules (mainly dipalmitoylphosphatidylcholine) insert into the alveolar fluid film and disrupt cohesive forces, lowering T.
- By Laplace’s law, if T decreases, the inflation pressure P required to prevent alveolar collapse decreases proportionally (P ∝ T).
- With a smaller pressure needed to achieve a given volume (ΔP reduced), compliance (ΔV/ΔP) increases.

3) Numerical illustration:
- If T initially = 50 units, for a given radius r the required P = 2·50/r = 100/r.
- If surfactant lowers T to 25 units, P = 2·25/r = 50/r — the pressure halves, so the same volume change requires half the pressure, doubling compliance.

4) Why the correct answer is correct:
- Because surfactant lowers T, collapsing pressure and work of breathing fall; lungs are easier to inflate (increased compliance).

5) Why the other options are incorrect:
- Saying surfactant increases surface tension is opposite its biochemical action; that would increase collapsing pressure and reduce compliance.
- Saying surfactant decreases compliance misunderstands mechanics: reducing T lowers required pressure and therefore increases compliance, not decreases it.

Conclusion: The correct choices are “decrease” (alveolar surface tension) and “increase” (alveolar compliance), matching the provided answer.

The role of alveolar surfactant is to [ Select ] increase decrease the alveolar surface tension and to [ Select ] increase decrease alveolar compliance.多重下拉选择题

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