Exam #5: Gastric Motility

Question 1

What is the migrating motor complex?

Answer 1

GI motor activity that starts in the stomach and sweeps over the upper GI tract ~Q90min in the unfed state

Question 2

What are the three general types of motor activity in the stomach?

Answer 2

1) Storage= reservoir
2) Churning= mixing & initiation of digestion
3) Emptying= delivery of food to the duodenum

Question 3

What is receptive relaxation?

Answer 3

This is a vagovagal reflex that is initiated by swallowing; there is a reflexive relaxation of the stomach in anticipation of the food bolus

*****Allows for a rise in volume without a rise in pressure

Question 4

What mediates receptive relaxation?

Answer 4

Vagovagal reflex that is described as “Non-cholingeric/ Non-adrenergic”

Question 5

What does Non-cholingeric/ Non-adrenergic mean?

Answer 5

This is a kind of archaic term that typically refers to the action of NO, before it was known that NO played a role

Question 6

What is gastric accommodation?

Answer 6

This is stomach relaxation in response to gastric filling i.e. now stomach contents stretching the walls of the stomach lead to the release of NO that causes a relaxation of the stomach

Question 7

What are the two steps of gastric storing/ filling?

Answer 7

1) Receptive relaxation

2) Gastric accomodation

Question 8

What are the three parts of gastric churning?

Answer 8

1) Propulsion
2) Retropulsion
3) Grinding

Question 9

What is propulsion?

Answer 9

Movement of the contents toward the antrum/ pylorus

*****Note that the pylorus is closed

Question 10

What initiates propulsion?

Answer 10

Pacemaker cells near the greater curvature

Question 11

What happens after propulsion?

Answer 11

Propulsion of food against the closed pylorus results in pulverization and shearing of food

Question 12

What is grinding?

Answer 12

This is the process by which food is trapped in the antrum & food products smaller than 2mm pass through the pylorus

Question 13

What determines the rate of gastric emptying?

Answer 13

Content of the ingested material

• Liquid is fastest
• Glucose solution
• Protein and fat breakdown slowest

Question 14

What controls the rate of gastric emptying?

Answer 14

Neuronal & hormonal regulation

Question 15

What are the hormones that control gastric emptying? Summarize the stimuli that cause their secretion.

Answer 15

Secretin= HCl- duodenum
CCK= Fat- duodenum 
Gastrin= Protein- stomach

Question 16

What is the stimulus for Secretin secretion? What is the function of Secretin?

Answer 16

• HCl in duodenum results in delayed gastric emptying

- This is a protective

Question 17

What is the stimulus for CCK secretion? What is the function of CCK?

Answer 17

• Fat in the duodenum stimulates the release of CCK
• CCK feedback delays gastric emptying

This allows for efficient breakdown of the meal & increases the surface area for digestion

Question 18

What is the stimulus for Gastrin secretion? What is the function of Gastrin?

Answer 18

• Protein in the stomach induces the release of gastrin

- Gastrin delays gastric emptying to increase the efficiency of protein digestion in the stomach

Question 19

What is the role of duodenal distension?

Answer 19

Duodenal distention results in negative feedback on the stomach mediated by the ENS to delay gastric emptying

Question 20

What are the effect of ACh, opoids, and 5-HT on gastric emptying?

Answer 20

Delay

Question 21

What is the effect of NO & VIP on gastric emptying?

Answer 21

Promotion of gastric emptying

Question 22

What is gastroparesis?

Answer 22

Simply, gastroparesis= impaired motility

**Note that this is NOT a COMPLETE PARALYSIS; rather, a disruption of normal coordinated activity that leads to a delay in emptying that is more often NEURONAL in origin (vs. hormonal)

Question 23

Outline the emetic response.

Answer 23

1) Numerous peripheral stimuli converge on the emetric center in the medulla
2) Vomiting reflex
- reverse peristalsis in small intestine
- relax stomach
- forced inspiration
- sphincter relaxation
- expulsion

*****This reflex is under the control of: 5-HT, ACh, DA & Histamine

Question 24

Why is there increased salivary secretion prior to an emetic event?

Answer 24

This increased salivary production is protective, as it contains:

• HCO3-
• Mucin

Question 25

What are the molecular mechanisms that coordinate vomiting?

Answer 25

5-HT*, DA, ACh, & Histamine

Question 26

What are potentially good anti-emetic agents?

Answer 26

Drugs that block 5-HT, DA, ACh, and histamine