6.1 Motility of the GI Tract (Lecture)

Question 1

Which part of the stomach will have more forceful, more frequent contractions?

Answer 1

The part of the stomach that is most caudad, closest to the pylorus.

Question 2

Which nerve innervates most of the muscles of mastication?

Answer 2

The trigeminal nerve / Cranial nerve V.

Question 3

What is the maximum frequency of slow waves in the stomach?

Answer 3

3 – 5 waves per minute

Question 4

What hormone regulates the migrating myoelectric complex?

Answer 4

Motilin

Question 5

What three things given increase action potentials and force of contraction in the stomach?

Answer 5

Parasympathetic activity (acetylcholine).

Gastrin.

Motilin.

Question 6

What cells are thought of as of the pacemaker for the slow waves of the G.I. system?

Where are they located?

Answer 6

Interstitial cells of Cajal.

In the myenteric plexus (Auerbach’s) between the outer and inner layers of the muscularis externae.

Question 7

What are the three mechanisms for negative feedback of the duodenum to the stomach – decreasing gastric emptying?

Answer 7

Acid in the duodenum stimulates secretin which inhibits gastrin – thereby inhibiting gastric emptying.

Fats in the duodenum stimulate cholecystokinin and glucose-dependent insulinotropic peptide – which directly inhibit stomach motility.

Hypertonicity in the duodenum (overfull duodenum) directly inhibits gastric emptying through an unknown hormone.

Question 8

What three things given decrease frequency of action potentials and force of contraction of the stomach?

Answer 8

Sympathetic activity (norepinephrine).

Secretin.

Glucose-dependent insulinotropic peptide (GIP).

Question 9

What is released by enterochromaffin -like cells to initiate peristalsis?

What is the receptor for that molecule?

Answer 9

Enterochromaffin -like cells produce serotonin.

This serotonin binds to receptors on intrinsic primary afferent neurons.

Question 10

Which nerves transmit afferent signal in the vomiting reflex?

Answer 10

The vagal afferents or the sympathetic afferents.

Question 11

What part of the central nervous system controls the involuntary swallowing reflex?

Answer 11

The swallowing center of the medulla.

Question 12

Which neurotransmitters are released in the circular muscle behind the bolus during peristalsis?

Answer 12

Excitatory transmitters acetylcholine, substance P, and neuropeptide Y.

(Note that these transmitters are inhibited in the longitudinal muscle behind the bolus)

Question 13

Which part of the stomach is less responsible for the mixing of food, and more responsible for accommodation of food?

Answer 13

The orad region.

Question 14

What is receptive relaxation?

Answer 14

The phenomenon by which the orad region of the stomach relaxes receptively with the lower esophageal sphincter.

Question 15

What part of the central nervous system coordinates the chewing reflex?

Answer 15

The brainstem.

Question 16

What is the migrating myoelectric complex?

Answer 16

The migrating myoelectric complex is a sort of housekeeping that occurs during fasting. It consists of large bursting peristaltic contractions throughout the stomach (including the orad region, which is normally quiet).

Question 17

Which nerves carry afferent sensory information to the medullary swallowing center?

Answer 17

The glossopharyngeal and vagus nerves.

Question 18

How do slow waves generate a contraction?

Answer 18

The depolarization occurs in a slow arc, and when it reaches threshold, action potentials occur. These action potentials cause contraction.

Question 19

Where’s the vomiting center of the brain located?

Answer 19

In the medulla

Question 20

What is different about the slow waves and their relationship with muscle contraction in the stomach vs. the small intestine?

Answer 20

Slow waves in the small intestine do not themselves initiate contractions, unlike in the stomach.

In the small intestine they can only set the frequency of contractions.

Question 21

What are the steps of the vomiting reflex physically?

Answer 21

Reverse peristalsis, forced inspiration, movement of the larynx, lower esophageal sphincter relaxation, closure of the glottis, and ultimately a forceful expulsion of gastric contents.

Question 22

What is the slow wave frequency in the duodenum, jejunum, and ileum?

Answer 22

Duodenum: 12.

Jejunum: 10.

Ileum: 8.

Question 23

What neurotransmitter causes the lower esophageal sphincter to relax in response to an approaching food bolus?

What releases this neurotransmitter?

Answer 23

Vasoactive intestinal peptide.

Fibers of the vagus nerve.

Question 24

What initiates the primary and secondary peristaltic waves in the esophagus respectively?

Answer 24

The primary peristaltic wave of the esophagus is initiated by the swallowing reflex of the medulla.

The secondary peristaltic wave is initiated in the case that the primary peristaltic wave does not clear the esophagus of food, and is initiated by the myenteric (Auerbach’s) plexus.

Question 25

What are the steps involved in the pharyngeal phase of swallowing?

Answer 25

First, the soft palate is pulled upwards moving the epiglottis.

Then the upper esophageal sphincter relaxes.

Then the pharynx initiates a peristaltic wave of contractions to push food into the esophagus.

Question 26

What nerves of the parasympathetic nervous system are responsible for which portions of the large intestine?

Answer 26

The vagus nerve is responsible for the cecum, ascending colon, and transverse colon.

The pelvic nerves are responsible for the descending colon, sigmoid colon, and rectum.

Question 27

What neurotransmitters are released in the circular muscle in front of the bolus during peristalsis?

Answer 27

Inhibitory transmitters vasoactive intestinal peptide, and nitric oxide.

(Note that these are what are inhibited in the longitudinal muscle in front of the bolus.)

Question 28

How is peristalsis different in the large intestine than the small intestine?

Answer 28

The large intestine utilizes mass movement, which occurs only one to three times per day

Question 29

What is the function of cholecystokinin on the orad region of the stomach?

Answer 29

Decreases gastric contractions and increases gastric distensibility.

Question 30

Which nerve controls the internal anal sphincter?

Which nerve controls the external anal sphincter?

Answer 30

Internal anal sphincter – pelvic splanchnic nerve.

External anal sphincter – pudendal nerve.

Question 31

How does receptive relaxation occur?

Answer 31

Release of vasoactive intestinal peptide via the vasovagal reflex.

Question 32

Where are the somatosensory receptors which trigger the swallowing reflex located?

Answer 32

Near to the pharynx.

Question 33

Which nerves of the sympathetic nervous system are responsible for which portions of the large intestine?

Answer 33

Superior mesenteric ganglion is responsible for the proximal regions.

Inferior mesenteric ganglion is responsible for the distal regions.

Hypogastric plexus is responsible for the distal rectum and anal canal.

Question 34

What is the purpose of the intrinsic primary afferent neurons in peristalsis?

Answer 34

When activated by serotonin from the enterochromaffin-like cells, they initiate the peristaltic reflex in that segment of the small intestine.

Question 35

What cells sense the food bolus in the intestinal lumen?

Histologically, where are these cells located?

Answer 35

Enterochromaffin-like cells.

The intestinal submucosa.

Question 36

Which peristaltic wave cannot occur after a vagotomy?

Answer 36

The primary peristaltic wave.

The primary peristaltic wave relies on sensory information carried by the vagus nerve to the medulla.

Question 37

What is the enterogastric reflex?

Answer 37

Feedback mechanisms from the duodenum modifying the rate of stomach emptying.