Endocrinology: thyroid hormone actions: 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.

Try it

Physiology · Endocrinology: thyroid hormone actions

Sample item

A woman with thyrotoxicosis has resting tachycardia, heat intolerance and raised oxygen consumption although plasma catecholamines are normal. Which actions of thyroid hormone explain these findings?

AInhibition of mitochondrial oxidative phosphorylationBIncreased adrenal secretion of adrenalineCUpregulation of beta-adrenergic receptors and increased synthesis of Na-K ATPaseDReduced expression of Na-K ATPase with less heat production

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

The answer and the reasoning

C. Upregulation of beta-adrenergic receptors and increased synthesis of Na-K ATPase

Thyroid hormone raises basal metabolic rate partly by increasing the number of Na-K ATPase pumps, which consume ATP and generate heat. It also increases cardiac beta-receptor numbers, so heart rate and output rise despite normal catecholamine levels. This is why beta-blockers relieve many symptoms.

Option by option

A. Inhibition of mitochondrial oxidative phosphorylation
Oxidative phosphorylation is stimulated, with oxygen consumption rising.
B. Increased adrenal secretion of adrenaline
Catecholamine levels are normal; the sensitivity to them is increased.
C. Upregulation of beta-adrenergic receptors and increased synthesis of Na-K ATPase (correct)
Correct. Beta-receptor upregulation and more pumps increase heart rate and oxygen use.
D. Reduced expression of Na-K ATPase with less heat production
Pump expression is increased, not decreased, in thyrotoxicosis.

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, Upregulation of beta-adrenergic receptors and increased synthesis of Na-K ATPase. Thyroid hormone raises basal metabolic rate partly by increasing the number of Na-K ATPase pumps, which consume ATP and generate heat.

Why is "Inhibition of mitochondrial oxidative phosphorylation" not the answer?

Oxidative phosphorylation is stimulated, with oxygen consumption rising.

Why is "Increased adrenal secretion of adrenaline" not the answer?

Catecholamine levels are normal; the sensitivity to them is increased.

Why is "Reduced expression of Na-K ATPase with less heat production" not the answer?

Pump expression is increased, not decreased, in thyrotoxicosis.

What concept does this question test?

It tests Endocrinology: thyroid hormone actions in Physiology. It also increases cardiac beta-receptor numbers, so heart rate and output rise despite normal catecholamine levels. This is why beta-blockers relieve many symptoms.

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 Endocrinology: thyroid hormone actions?

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.