At birth, the ductus arteriosus normally closes within 10–15 hours. The primary stimulus for its functional closure in term neonates is:
- A Fall in pulmonary vascular resistance allowing reversal of flow through the ductus
- B Rise in PaO2 after first breath, causing smooth muscle contraction in the ductus wall ✓
- C Rise in prostaglandin E2 (PGE2) levels from the placenta
- D Bradykinin released from the ductus endothelium in response to pulmonary blood flow
Correct answer: B. Rise in PaO2 after first breath, causing smooth muscle contraction in the ductus wall
Explanation
The ductus arteriosus is maintained open in utero by prostaglandin E2 (PGE2) and low oxygen tension. At birth, the rise in PaO2 (from air breathing) directly constricts the oxygen-sensitive smooth muscle of the ductus arteriosus, causing functional closure within hours. Simultaneously, the placenta (a major source of PGE2) is delivered, removing the dilator stimulus. NSAIDs (indomethacin/ibuprofen) are used to close a patent ductus by inhibiting prostaglandin synthesis. Anatomical closure by fibrosis takes 2–3 weeks.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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