At birth, the newborn's lungs must expand and fill with air for the first time. The critical surfactant that lowers surface tension and prevents alveolar collapse (atelectasis) is predominantly synthesized from:
- A Dipalmitoylphosphatidylcholine (DPPC, lecithin) produced by type II pneumocytes, mature by 35–36 weeks gestation ✓
- B Sphingomyelin from type I pneumocytes, mature by 28 weeks
- C Cholesterol esters from alveolar macrophages
- D Glycoproteins secreted by Clara cells (club cells) in the terminal bronchioles
Correct answer: A. Dipalmitoylphosphatidylcholine (DPPC, lecithin) produced by type II pneumocytes, mature by 35–36 weeks gestation
Explanation
Pulmonary surfactant is composed primarily of dipalmitoylphosphatidylcholine (DPPC, lecithin) along with phosphatidylglycerol, surfactant apoproteins (SP-A, SP-B, SP-C, SP-D), and neutral lipids. It is synthesized and secreted by type II alveolar pneumocytes. DPPC production matures by approximately 35–36 weeks gestation; the lecithin-to-sphingomyelin (L/S) ratio of ≥2 in amniotic fluid indicates pulmonary maturity. Before this, the insufficient surfactant causes respiratory distress syndrome (hyaline membrane disease) in premature infants.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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