Lecture 4 : Gastric Motility

Question 1

What is GI Motility

Answer 1

• Coordinated contractions and relaxations of GI Tract moving contents from motu to anus

3 main pattern :
- Peristalsis
- Segmentation
- Tonic Contraction

2 Types of muscles, Skeletal (voluntary) and smooth (involuntary)

Smooth muscle found throughout GI Tract, 2 layers, inner (circular) and outer (longitudinal)

Skeletal muscles mainly found in pharynx, top 2 thirds of esophagus, and external anal sphincter

Question 2

Smooth Muscle Phasic and Tonic contractions diagram

Answer 2

Question 3

What does activation of myenteric and submucosal plexus do?

Answer 3

Myenteric Plexus activation
- Increases tonic (rapid) contractions
- Velocity of contents of GI Tract increases

Submucosal Plexus activation
- Increases secretory activity
- Modulates intestinal absorption

Question 4

Gastric Motility - FOOD STORAGE

Answer 4

• Empty stomach - 50ml
• Food is swallowed, smooth muscles in fundus relax before food arrives, stimulated by vago-vagal reflex (receptive relaxation)
• Stomach vol increases to 1.5L with little increase in pressure

Question 5

Gastric Motility - PROPULSION

Answer 5

When bolus is moved towards antrum via gastric contractions and occlusion of pylorus, all together called propulsion.

Sieving function is when liquids and smaller particles leave stomach more rapidly than larger particles.

Question 6

Gastric Motility - GRINDING

Answer 6

Once bolus trapped near antrum, it is churned to help reduce size of particles, called GRINDING

Only particles less than 2mm are propelled through pylorus into duodenum

Question 7

Gastric Motility - RETROPULSION

Answer 7

When larger particles in antrum returned to corpus for further breakdown.

Propulsion -> Grinding -> Repopulsion, cycle repeats til stomach is emptied.

Question 8

Summary of Propulsion, Grinding and Retropulsion

Answer 8

Question 9

What is gastric emptying

Answer 9

Process by which contents of stomach are emptied into duodenum.

Regualted by autonomic nervous system (vagus nerve) and GI hormones.

Pyrolic sphincter allows carefully regulated emptying of gastric contents and prevents regurgitation of duodenal contents.

Question 10

3 Phases of gastric emptying

Answer 10

Cephalic Phase
- Food in mouth
- Inhibitory nerve fibres in vagus nerve cause relaxation of stomach, allowing it to take large volumes of food

Gastric Phase
- Food in stomach
- Excitatory phase, stomach empties at a rate proportional to the volume of it
- Stretching stomach causes myogenic reflex, activating vagus nerve via pressure receptors, causing contraction
- Gastrin is released in response to peptides in stomach, enhancing acid secretion and stimulating more smooth muscle contraction,

Intestinal Phase
- Food in duodenum, ileum or colon
- Inhibitory phase
- Controlled by hormonal and paracrine mechanisms

Low pH = activation of secretin
High fats / lipids = increased secretion of CCK
High levels of amino acids = Increased secretion of gastrin
High levels of carbs = Increased secretion of gastric inhibitory peptides

• SOme motor reflexes too, ileogastric reflex

Question 11

How is motility of the stomach regulated summary

Answer 11

Question 12

Gastropariesis

Answer 12