Adrenal: steroid biosynthesis: 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 · Adrenal: steroid biosynthesis

Sample item

A 10-day-old boy has vomiting, weight loss, serum sodium 123 mmol/L, potassium 6.4 mmol/L and hyperpigmented genitalia. Deficiency of 21-hydroxylase is suspected. Which hormone level is markedly raised in the blood?

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

The answer and the reasoning

D. 17-hydroxyprogesterone

Without 21-hydroxylase, 17-hydroxyprogesterone and progesterone cannot be converted to 11-deoxycortisol and 11-deoxycorticosterone. Cortisol and aldosterone fall, producing salt-wasting, while ACTH rises and drives androgen production. The raised 17-hydroxyprogesterone is the diagnostic marker used in newborn screening.

Option by option

  • A. Cortisol

    Cortisol is low because its synthesis is blocked.

  • B. 11-deoxycorticosterone only

    11-deoxycorticosterone is also reduced, because it also needs 21-hydroxylation.

  • C. Aldosterone

    Aldosterone is low, causing salt wasting with hyperkalaemia.

  • D. 17-hydroxyprogesterone (correct)

    Correct. The substrate before the block accumulates.

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 D, 17-hydroxyprogesterone. Without 21-hydroxylase, 17-hydroxyprogesterone and progesterone cannot be converted to 11-deoxycortisol and 11-deoxycorticosterone.

Why is "Cortisol" not the answer?

Cortisol is low because its synthesis is blocked.

Why is "11-deoxycorticosterone only" not the answer?

11-deoxycorticosterone is also reduced, because it also needs 21-hydroxylation.

Why is "Aldosterone" not the answer?

Aldosterone is low, causing salt wasting with hyperkalaemia.

What concept does this question test?

It tests Adrenal: steroid biosynthesis in Physiology. Cortisol and aldosterone fall, producing salt-wasting, while ACTH rises and drives androgen production. The raised 17-hydroxyprogesterone is the diagnostic marker used in newborn screening.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Adrenal: steroid biosynthesis?

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.