Embryology: laterality: 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: laterality

Sample item

A 25-year-old man with recurrent sinusitis, bronchiectasis and infertility has dextrocardia on chest radiograph. A defect in which structure best explains the abnormal looping of the heart?

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

The answer and the reasoning

A. Dynein arms of nodal cilia

Primary ciliary dyskinesia (Kartagener syndrome) arises from defective dynein arms of cilia. Rotating nodal cilia generate the leftward flow that establishes left-right asymmetry, so about half of affected people have situs inversus. Immotile cilia and sperm tails explain sinusitis, bronchiectasis and infertility.

Option by option

  • A. Dynein arms of nodal cilia (correct)

    Correct. Dynein arm defects disrupt nodal flow and cause situs inversus with chronic respiratory disease.

  • B. Notochordal plate

    The notochordal plate patterns midline structures but is not the cause of this ciliary disorder.

  • C. Apical ectodermal ridge

    The apical ectodermal ridge guides limb outgrowth.

  • D. Neural crest cells

    Neural crest defects cause conotruncal and craniofacial anomalies.

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.

More Anatomy questions

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is A, Dynein arms of nodal cilia. Primary ciliary dyskinesia (Kartagener syndrome) arises from defective dynein arms of cilia.

Why is "Notochordal plate" not the answer?

The notochordal plate patterns midline structures but is not the cause of this ciliary disorder.

Why is "Apical ectodermal ridge" not the answer?

The apical ectodermal ridge guides limb outgrowth.

Why is "Neural crest cells" not the answer?

Neural crest defects cause conotruncal and craniofacial anomalies.

What concept does this question test?

It tests Embryology: laterality in Anatomy. Rotating nodal cilia generate the leftward flow that establishes left-right asymmetry, so about half of affected people have situs inversus. Immotile cilia and sperm tails explain sinusitis, bronchiectasis and infertility.

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: laterality?

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.