GI Mobility

Question 1

75% of parasympathetic innervation of the GI tract is via CN X. The rest is by which nerve?

Answer 1

Pelvic nerves

Question 2

Which neurotransmitters are involved in the propulsive segment of peristalsis?

Answer 2

Substance P and Acetylcholine

NOTE: The propulsive segment is the area behind the bolus. Pressure must increase to move the bolus foward.

Question 3

Which neurotransmitters are involved in the receiving segment of peristalsis?

Answer 3

NO and VIP

NOTE: The receiving segment is the area in front of the bolus. Circular muscles in the receiving segment must be relaxed in order to “receive” the segment.

Question 4

Explain how neural reflexes are involved in peristalsis.

Answer 4

• Distention is picked up on sensory neurons in the submucosal plexus, which carry signals via the cholinergic interneurons to the inhibitory motor neurons infront of the bolus.
  
  • This causes release of VIP and NO, so tht the circular muscles relax in the receiving segment.

Question 5

Motor Functions of the Stomach

Answer 5

Question 6

Gastric emptying in humans

Answer 6

Initially while you eat there is rapid emptying of the food, and this emptying slows down gradually from about 30 minutes to almost 60 minutes. The rate of motility is associated with the stomach.

Question 7

Jet retropulsion

Answer 7

Stomach’s contents pass through pyloric sphincter, which snaps closed. In the process, the sphincter pushes whatever didn’t pass through back into the stomach. This happens particularly when you don’t chew enough and just swallow big morsels of food.

Question 8

____________ initiates a defecation response.

Answer 8

Ano-rectal distension

Question 9

Involuntary defecation reflex

Answer 9

Propulsive motility of descending colon and rectum

Question 10

Voluntary defecation reflex

Answer 10

• Closure of glottis
• Descent of diaphragm
• Contraction of abdominal wall muscles

This leads to an increase in intraabdominal pressure

NOTE: Breathing against a closed glottis can be dangeous for cardiovascular patients, if they are constipated or straining to defecate. Because as you increase intrabdominal prssure, you also increase intrathoracic pressure, which in turn causes an increase in arterial pressure and perfusion of blood up to the brain. Stroke can possibly occur as a result.