COMEDK 2007 MCQ Answer 139
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The correct answer is A
Surfactant in the lung
Surfactant in the lung
- Secreted by Type II alveolar cells, surfactant lines the alveoli at the gas-liquid interface and has dipalmitoyl lecithin, (dipolmitoyl phosphotidyl choline=DPPC) as a major constituent.
- Surfactant has 2 unique surface tension properties
- The average surface tension is low.
- Surface tension varies with area. Surface tension rises as area gets bigger and falls as area gets smaller.
- Increases lung compliance because surface forces are reduced.
- Promotes alveolar stability and prevents alveolar collapse. Decreased surface area lowers surface tension. Increased surface area increases surface tension. Small alveoli are prevented from getting smaller. Large alveoli are prevented from getting bigger.
- Promotes dry alveoli. Alveolar collapse tends to “suck” fluid from pulmonary capillaries. Stabilizing alveoli (see b) prevents transudation of fluid by preventing collapse.
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