DPPC Surfactant Percentage — FRCA Primary MCQ

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ModeratePhysiology - RespiratoryDPPC Surfactant PercentageFRCA Primary

By mass, dipalmitoylphosphatidylcholine (DPPC) accounts for approximately what proportion of normal pulmonary surfactant?

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Correct answer: E — 50%

DPPC constitutes approximately half of pulmonary surfactant by mass and is its principal surface-active phospholipid. Its two saturated palmitoyl chains permit close molecular packing during expiration, allowing alveolar surface tension to fall to very low levels and helping prevent alveolar collapse. Therefore, 50% is the best approximation. Values near 75–90% describe broader lipid or phospholipid fractions rather than DPPC alone. Approximately 10% represents the protein fraction, including SP-A, SP-B, SP-C and SP-D. A value of 25% is too low for DPPC and is closer to estimates for other phosphatidylcholine species in traditional compositional descriptions.

Reference: King RJ. Pulmonary surfactant. Journal of Applied Physiology, 1982;53(1):1–8. https://pubmed.ncbi.nlm.nih.gov/6749772/