GI physiology: defecation: 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 · GI physiology: defecation

Sample item

A man feels the urge to defecate during a meeting. The rectum is distended and the internal anal sphincter relaxes reflexly. What allows him to maintain continence?

AInhibition of the enteric nervous system by the hypogastric nerveBContraction of the internal anal sphincter through the pelvic splanchnic nervesCRelaxation of the puborectalis muscleDVoluntary contraction of the external anal sphincter through the pudendal nerve

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

The answer and the reasoning

D. Voluntary contraction of the external anal sphincter through the pudendal nerve

Rectal distension triggers the rectoanal inhibitory reflex, a relaxation of the internal sphincter mediated by enteric neurons. The external sphincter is skeletal muscle supplied by the pudendal nerve (S2 to S4) and can be contracted voluntarily to defer defecation. The puborectalis keeps the anorectal angle, and contracts to maintain continence.

Option by option

A. Inhibition of the enteric nervous system by the hypogastric nerve
The hypogastric nerve is sympathetic and is not the pathway of voluntary control.
B. Contraction of the internal anal sphincter through the pelvic splanchnic nerves
The internal sphincter is relaxed by this reflex, and parasympathetic activity promotes emptying.
C. Relaxation of the puborectalis muscle
Relaxation of puborectalis straightens the anorectal angle and facilitates defecation.
D. Voluntary contraction of the external anal sphincter through the pudendal nerve (correct)
The external sphincter is under voluntary control through the pudendal nerve.

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 D, Voluntary contraction of the external anal sphincter through the pudendal nerve. Rectal distension triggers the rectoanal inhibitory reflex, a relaxation of the internal sphincter mediated by enteric neurons.

Why is "Inhibition of the enteric nervous system by the hypogastric nerve" not the answer?

The hypogastric nerve is sympathetic and is not the pathway of voluntary control.

Why is "Contraction of the internal anal sphincter through the pelvic splanch…" not the answer?

The internal sphincter is relaxed by this reflex, and parasympathetic activity promotes emptying.

Why is "Relaxation of the puborectalis muscle" not the answer?

Relaxation of puborectalis straightens the anorectal angle and facilitates defecation.

What concept does this question test?

It tests GI physiology: defecation in Physiology. The external sphincter is skeletal muscle supplied by the pudendal nerve (S2 to S4) and can be contracted voluntarily to defer defecation. The puborectalis keeps the anorectal angle, and contracts to maintain continence.

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 GI physiology: defecation?

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.