Fetal circulation: ductus arteriosus: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Fetal circulation: ductus arteriosus

Sample item

In a healthy full-term newborn, functional closure of the ductus arteriosus occurs within the first days of life. Which change is mainly responsible?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Rise in arterial PO2 and fall in prostaglandin E2 levels

In the fetus, low oxygen tension and high prostaglandin E2 from the placenta keep the ductus open. After birth the first breaths raise arterial PO2 and the placental source of prostaglandins is lost, so the ductal smooth muscle constricts. This is why indomethacin closes a patent ductus while prostaglandin E1 keeps it open in duct-dependent lesions.

Option by option

  • A. Rise in arterial PO2 and fall in prostaglandin E2 levels (correct)

    Correct. Oxygen constricts the ductus and low prostaglandin levels remove the dilating stimulus.

  • B. Fall in arterial PO2 after the first breath

    A fall in PO2 would maintain ductal patency, as in the fetus.

  • C. Rise in circulating prostaglandin E2

    Prostaglandin E2 keeps the ductus open, so a rise would prevent closure.

  • D. Rise in pulmonary vascular resistance

    Pulmonary vascular resistance falls after birth, which increases pulmonary flow and reverses the shunt.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is A, Rise in arterial PO2 and fall in prostaglandin E2 levels. In the fetus, low oxygen tension and high prostaglandin E2 from the placenta keep the ductus open.

Why is "Fall in arterial PO2 after the first breath" not the answer?

A fall in PO2 would maintain ductal patency, as in the fetus.

Why is "Rise in circulating prostaglandin E2" not the answer?

Prostaglandin E2 keeps the ductus open, so a rise would prevent closure.

Why is "Rise in pulmonary vascular resistance" not the answer?

Pulmonary vascular resistance falls after birth, which increases pulmonary flow and reverses the shunt.

What concept does this question test?

It tests Fetal circulation: ductus arteriosus in Physiology. After birth the first breaths raise arterial PO2 and the placental source of prostaglandins is lost, so the ductal smooth muscle constricts. This is why indomethacin closes a patent ductus while prostaglandin E1 keeps it open in duct-dependent lesions.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Fetal circulation: ductus arteriosus?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.