Motility and peristalsis · Physiology

How do opioid medications (like morphine) typically affect gastrointestinal motility?

  1. They stimulate the myenteric plexus and boost peristalsis
  2. They block excitatory transmitters, causing constipation
  3. They raise the frequency of gastric slow waves
  4. They rapidly relax the internal anal sphincter muscle
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Correct answer: They block excitatory transmitters, causing constipation

Opioids bind to mu-receptors in the enteric nervous system, which inhibits the release of acetylcholine. This decreases propulsive motility and increases fluid absorption, leading to opioid-induced constipation.

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