Surfactant start synthesis in 20-24w o· docto increase in 28-32w J八∧ meet demands after 35w bodle body Y double in alveolar within 24h Type I ca adult level after 3-7d s- TyPe l Cell √haf-life12~24h Blood v renew in 24-48, >90% reuse Type I CellSurfactant ✓start synthesis in 20~24w ✓increase in 28~32w ✓meet demands after 35w ✓double in alveolar within 24h ✓adult level after 3~7d ✓half-life 12~24h ✓renew in 24~48,>90% reuse