Gastrointestinal Lecture 2 Part 2 Segment Specific Patterns of Motility (Mouth and Stomach)

Question 1

Segment-specific motility in the mouth

Answer 1

• Chewing → mastication
• Swallowing

Question 2

Chewing

Answer 2

Motile function

• Voluntary
• Breaks up large food particles
• Mixes ingested food with saliva to lubricate it
• Aids swallowing

Question 3

Swallowing

Answer 3

Pushing food bolus to back of mouth

• Reflex response
• Involuntary contraction of the esophagus (peristaltic wave), that propels food to the stomach

Question 4

Phases of segment-specific motility in the stomach

Answer 4

1. Activity of the lower esophageal sphincter
2. gastric motility
3. Gastric emptying (activity of the pyloric sphincter)
4. Belching and vomiting

Question 5

LES

Answer 5

Lower esophageal sphincter

Question 6

Activity of the lower esophageal sphincter

Answer 6

• Tonically active, but relaxes on swallowing to allow entrance of food bolus to stomach
• Contracts in response to acetylcholine relaxes in response to NO (nitric oxide) and VIP (vasoactive intestinal peptide)
• Tonic activity prevents reflux of stomach contents into the esophagus

Question 7

Three major components of LES

Answer 7

1. Internal sphincter – thickening of esophageal smooth muscle
2. External sphincter – crural portion of the diaphragm surrounds the esophagus
3. Clasp and sling fibers – muscles of stomach wall → Wrap around esophageal sphincter and help to constrict it

Question 8

Arrival of food bolus in the stomach characterized by…?

Answer 8

receptive relaxation → walls relax as volume increases

• relaxation of the stomach to allow increase in volume with marginal increase in pressure (Empty stomach = 50 mL, full stomach = 1.5 L)

Question 9

Basal tone

Answer 9

In anatomy, denoting a layer or cells farthest away from the surface; the muscle’s resistance to passive stretch during resting state

Question 10

What happens with overfilling the stomach

Answer 10

Relaxation of the stomach (aka compliance) has its limits, and overfilling can cause belching or even vomiting (case reports of stomach rupture do exist)

Question 11

function of peristalsis in gastric motility and emptying

Answer 11

Gastric peristalsis mixes the stomach contents and pushes food through the pyloric sphincter

• Peristaltic wave initiates at upper part of stomach
• Wave increases in size as it moves down the stomach, mixing the contents and forcing the pyloric sphincter closed
• a small volume of liquid chyme is forced through the pyloric sphincter

Question 12

How is peristalsis generated in the stomach?

Answer 12

• Gastric peristalsis generated by basic electrical rhythm (~3/min; as introduced earlier)
  
  • rhythm is stable, but force of contraction controlled (and therefore strength of mixing and emptying influenced by extrinsic factors)

Question 13

Extrinsic factors controlling gastric emptying:

Answer 13

• Stomach and intestinal contents
• Acidity
• Distension
• Hypertonicity

Question 14

What stomach contents effect gastric emptying?

Answer 14

Meals rich in protein or fat will delay gastric emptying (increase satiety) vs. carbs.

Question 15

How does acidity effect gastric emptying?

Answer 15

A feedback loop exists between the small intestine and stomach; exposure of the duodenum to lots of acidity inhibits gastric emptying because it can only neutralize small amounts at a time

Question 16

How does distension affect gastric emptying?

Answer 16

• Distension of stomach increases peristaltic contractions, therefore after a large meal stomach contractions are greater, thereby increasing gastric emptying
• On the other hand, distension of the duodenum will inhibit gastric emptying

Question 17

How does hypertonicity affect gastric emptying?

Answer 17

Gastric emptying is fastest when duodenal contents are isotonic. Gastric chyme can be hyperosmolar. A hypertonic solution in the duodenum will inhibit gastric emptying, this prevents fluid in the duodenum becoming too hypertonic (therefore affecting water absorption in the small intestine).

• Control for acidity, volume and hypertonicity

Question 18

Belching

Answer 18

Air unavoidably swallowed during eating and drinking (aerophagia) - Some of this air is regurgitated by belching causing “physiological venting of excessive gastric air”

Question 19

physiological response of belching

Answer 19

Air in the stomach increases gastric volume, initiating a reflex response that relaxes the lower esophageal sphincter allowing the gas to escape

Question 20

Vomitting

Answer 20

Involuntary, forceful expulsion of stomach contents via the mouth

Question 21

Physiological response for vomitting

Answer 21

• Centrally regulated
• Typically preceded by salivation and nausea
• Reverse peristalsis starts from the intestine and sweeps upwards
• The glottis closes to prevent aspiration and protect the trachea/lungs
• Contraction of abdominal wall muscles increases abdominal pressure
• Sphincters and esophagus relax, allowing passage of stomach contents

Question 22

Triggers of vomitting

Answer 22

Different triggers act through different neural pathways to elicit vomiting response

• digestive (gastroenteritis, bowel obstruction, food allergy)
• sensory (motion sickness, viral infection, morning sickness, drug reaction [inc. alcohol])
• emetics (medically administered to prevent poisoning)
• Social cues
• Miscellaneous (nauseating sights/smells, anxiety)