Embryology: ostium primum defect: practice question

A Anatomy 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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Anatomy · Embryology: ostium primum defect

Sample item

An infant with Down syndrome has a murmur, and echocardiography shows an atrial septal defect low in the septum with a cleft anterior mitral leaflet. Which embryonic structure is deficient?

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

The answer and the reasoning

D. Endocardial cushions

Fusion of the superior and inferior endocardial cushions divides the atrioventricular canal and contributes to the lower atrial septum, upper ventricular septum and mitral and tricuspid leaflets. Deficient cushions cause an ostium primum defect with a mitral cleft, common in trisomy 21.

Option by option

  • A. Bulbar ridges

    Bulbar ridges form the conotruncal septum, not the cushion-derived lower atrial septum.

  • B. Aorticopulmonary septum

    The aorticopulmonary septum divides the truncus and does not affect the atrioventricular canal.

  • C. Septum secundum

    A septum secundum defect is higher and does not involve the mitral valve.

  • D. Endocardial cushions (correct)

    Correct. Endocardial cushion deficiency causes this low atrial defect with a cleft mitral valve.

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 Anatomy question

What is the answer to this Anatomy question?

The best answer is D, Endocardial cushions. Fusion of the superior and inferior endocardial cushions divides the atrioventricular canal and contributes to the lower atrial septum, upper ventricular septum and mitral and tricuspid leaflets.

Why is "Bulbar ridges" not the answer?

Bulbar ridges form the conotruncal septum, not the cushion-derived lower atrial septum.

Why is "Aorticopulmonary septum" not the answer?

The aorticopulmonary septum divides the truncus and does not affect the atrioventricular canal.

Why is "Septum secundum" not the answer?

A septum secundum defect is higher and does not involve the mitral valve.

What concept does this question test?

It tests Embryology: ostium primum defect in Anatomy. Deficient cushions cause an ostium primum defect with a mitral cleft, common in trisomy 21.

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 Embryology: ostium primum defect?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy 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.