Adrenal: ACTH and pigmentation: 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: ACTH and pigmentation

Sample item

A 38-year-old woman with tuberculous adrenalitis has hypotension, hyponatraemia and hyperpigmentation of the palmar creases and buccal mucosa. Why does skin pigmentation increase?

AReduced renin activity increases melanin productionBRaised aldosterone stimulates melanocyte proliferationCHigh ACTH from the pro-opiomelanocortin precursor stimulates melanocytesDExcess cortisol directly stimulates melanin synthesis

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

The answer and the reasoning

C. High ACTH from the pro-opiomelanocortin precursor stimulates melanocytes

In primary adrenal failure, low cortisol removes negative feedback and ACTH rises. ACTH and melanocyte-stimulating hormone are both cleaved from pro-opiomelanocortin, and ACTH itself has melanocortin-1 receptor activity, so melanin production increases. Pigmentation is therefore absent in secondary adrenal failure from pituitary disease.

Option by option

A. Reduced renin activity increases melanin production
Renin is raised, not reduced, and it has no role in pigmentation.
B. Raised aldosterone stimulates melanocyte proliferation
Aldosterone is also low in primary adrenal failure and has no pigment action.
C. High ACTH from the pro-opiomelanocortin precursor stimulates melanocytes (correct)
Correct. High ACTH acts on melanocytes through the melanocortin receptor.
D. Excess cortisol directly stimulates melanin synthesis
Cortisol is low in this condition, and it does not stimulate melanocytes.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, High ACTH from the pro-opiomelanocortin precursor stimulates melanocytes. In primary adrenal failure, low cortisol removes negative feedback and ACTH rises.

Why is "Reduced renin activity increases melanin production" not the answer?

Renin is raised, not reduced, and it has no role in pigmentation.

Why is "Raised aldosterone stimulates melanocyte proliferation" not the answer?

Aldosterone is also low in primary adrenal failure and has no pigment action.

Why is "Excess cortisol directly stimulates melanin synthesis" not the answer?

Cortisol is low in this condition, and it does not stimulate melanocytes.

What concept does this question test?

It tests Adrenal: ACTH and pigmentation in Physiology. ACTH and melanocyte-stimulating hormone are both cleaved from pro-opiomelanocortin, and ACTH itself has melanocortin-1 receptor activity, so melanin production increases. Pigmentation is therefore absent in secondary adrenal failure from pituitary disease.

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 Adrenal: ACTH and pigmentation?

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.