Motility and peristalsis · Physiology

During a peristaltic reflex, what occurs in the segment of the intestine located immediately downstream (anal-ward) of the bolus?

  1. Contraction of circular muscle and relaxation of longitudinal muscle
  2. Relaxation of circular muscle and contraction of longitudinal muscle
  3. Simultaneous contraction of both muscle layers
  4. No change in muscle tone occurs
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Correct answer: Relaxation of circular muscle and contraction of longitudinal muscle

To allow the bolus to move forward, the 'receptive relaxation' downstream involves the relaxation of the circular muscle layer. Concurrently, the longitudinal muscle contracts to shorten the segment, a process mediated primarily by inhibitory neurotransmitters like nitric oxide (NO) and VIP.

Difficulty: Medium Question 24 of 40

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