Gastrointestinal Motility

Question 1

What are the 3 phases of the body’s response to food?

Answer 1

Cephalic, gastric and intestinal

Question 2

Describe the cephalic phase of food exposure

Answer 2

Though, sight, smell and taste work to prepare GI tract through saliva, gastric acid and pancreatic secretion as well as inhibition of migrating motor complexes, gastrin and ghrelin secretion

Question 3

Describe the gastric phase of food exposure

Answer 3

Satiation and early digestion triggered by mechanical effect

Question 4

Describe the intestinal phase of food exposure

Answer 4

Feedback and satiation triggered mainly by chemoreceptor activation in the small bowel

Question 5

What happens during hunger in the GI tract?

Answer 5

There are there phases of contraction every 90-120 minutes which works to clear undigested material, prevent bacteria overgrowth and create hunger sensations

Question 6

How does the initiation of migrating motor complexes differ between the stomach and the small intestine?

Answer 6

Stomach is vagus-dependent and the small intestine is vagus-independent

Question 7

How does food move through the oesophagus?

Answer 7

Primary peristaltic wave occurs on swallowing due to contraction of striated muscle (vagus nerve), stretch receptors are then stimulated and a local reflex causes a secondary peristaltic wave which forces the bolus into the stomach as the LOS relaxes

Question 8

What is involved in receptive relaxation?

Answer 8

The vago-vagal reflexes causes the release of CCK

Question 9

What is involved in adaptive relaxation?

Answer 9

Enteric reflex releases NO from the ENS

Question 10

What are interstitial cells of Cajal (ICCs)?

Answer 10

Cells around the myenteric plexus within stomach muscle and colon and around the submucosal plexus of the colon; they create rhythm of electrical slow waves to cause phasic muscle contractions

Question 11

Name the three stages of gastric emptying

Answer 11

propulsion, emptying and retropulsion

Question 12

Describe the process of gastric emptying

Answer 12

Propulsion: rapid flow of liquids into stomach, delays flow of large particles towards pylorus
Emptying: liquids with small molecules are passed into duodenum whereas large particles are retained in a bulge in the terminal antrum
Retropulsion: movement into the antrum enables powerful contractions to further breakdown the particles, then there is clearing of the terminal antru

Question 13

What provides the extrinsic innervation of the gut?

Answer 13

Vagus nerve

Question 14

What causes gas build-up in the stomach?

Answer 14

Swallowing air (during eating/drinking) or due to increased swallowing due to increased salivation

Question 15

How is excess air released from the stomach?

Answer 15

LOS relaxes –> burp –> reduces stomach pressure –> avoids early satiety

Question 16

Describe the role of enteric sensory neurones

Answer 16

Have mechanical and chemosensitive receptors which respond to an intraluminal signal –> information transmitted via interneurons to motor neurones which secrete NO and/or ACh and this initiates the peristaltic reflex and modulates immune, vascular, muscular and epithelial transport systems

Question 17

What is defecation normally prevented by?

Answer 17

Tone of internal anal sphincter, puborectalis muscle and mechanical effects of acute anorectal angle

Question 18

What initiates defecation?

Answer 18

Puborectalis muscle and external anal sphincter relax and intra-abdominal pressure is increased by squatting in preparation

Question 19

What executes defecation?

Answer 19

Sphincter relaxation and rectal propulsive contractions