Histology: cilia ultrastructure: 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 · Histology: cilia ultrastructure

Sample item

A 28-year-old man has chronic sinusitis, bronchiectasis, dextrocardia on chest radiograph, and infertility with normal sperm count but immotile sperm. Electron microscopy of his respiratory cilia would classically show absence of which structure?

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

The answer and the reasoning

C. Dynein arms on the outer microtubule doublets

This is Kartagener syndrome, a form of primary ciliary dyskinesia. The axoneme has a 9+2 arrangement, and dynein arms provide the ATP-driven sliding that bends the cilium. Without them cilia and sperm tails are immotile, causing impaired mucociliary clearance, infertility and, because embryonic nodal cilia fail, randomised left-right asymmetry (situs inversus).

Option by option

  • A. Keratin intermediate filaments of the cell cortex

    Keratin filaments give mechanical strength to epithelia and are not part of the axoneme.

  • B. The actin filaments of the terminal web

    The terminal web is an apical actin network and is not the cause of immotile cilia.

  • C. Dynein arms on the outer microtubule doublets (correct)

    Correct. Absent dynein arms leave the cilia immotile, the classic defect in Kartagener syndrome.

  • D. Basal bodies at the base of each cilium

    Basal bodies anchor the cilia and are present; their loss would not be the classic finding.

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 C, Dynein arms on the outer microtubule doublets. This is Kartagener syndrome, a form of primary ciliary dyskinesia.

Why is "Keratin intermediate filaments of the cell cortex" not the answer?

Keratin filaments give mechanical strength to epithelia and are not part of the axoneme.

Why is "The actin filaments of the terminal web" not the answer?

The terminal web is an apical actin network and is not the cause of immotile cilia.

Why is "Basal bodies at the base of each cilium" not the answer?

Basal bodies anchor the cilia and are present; their loss would not be the classic finding.

What concept does this question test?

It tests Histology: cilia ultrastructure in Anatomy. The axoneme has a 9+2 arrangement, and dynein arms provide the ATP-driven sliding that bends the cilium. Without them cilia and sperm tails are immotile, causing impaired mucociliary clearance, infertility and, because embryonic nodal cilia fail, randomised left-right asymmetry (situs inversus).

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 Histology: cilia ultrastructure?

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.