The structure marked A begins to close by what time frame and due to what cause?: (A) Begins to close at 10-15 hours after bih, due to withdrawal of prostaglandins, (B) Begins to close at 10-15 hours after bih, due to expression of prostaglandins, (C) Begins to close 4 weeks after bih, due to fall in oxygen concentration, (D) Begins to close 4 weeks after bih, due to rise in oxygen tension
Answer is A. The structure marked is ductus aeriosus which begins to close 10-15 hours after bih due to withdrawal of prostaglandins and exhibits functional closure by 7 days and anatomical closure by 4 weeks after bih.