Lecithin
Summary
Common name for phosphatidylcholine, especially dipalmitoylphosphatidylcholine - the principal surface-tension-lowering phospholipid of pulmonary surfactant. The lecithin-to-sphingomyelin (L:S) ratio is the classic test of fetal lung maturity.
Detail
Surfactant is produced by type II pneumocytes and stored in lamellar bodies; lecithin rises sharply after ~35 weeks gestation while sphingomyelin remains relatively constant, so the L:S ratio increases with maturity. An L:S ratio >=2 predicts low risk of neonatal respiratory distress syndrome; <1.5 suggests immaturity. Maternal diabetes can falsely elevate the L:S ratio without true maturity, so phosphatidylglycerol is also assessed. Antenatal betamethasone or dexamethasone accelerates type II pneumocyte surfactant production in threatened preterm delivery. LCAT (lecithin-cholesterol acyltransferase) uses lecithin to esterify cholesterol in HDL.
Sources
- First Aid for USMLE Step 1 2024
- Lippincott Biochemistry
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