Motility in the GI tract

Question 1

What motor activity does the GI tract perform and its functions?

Answer 1

Segmental contractions (mixing)
Peristaltic contractions
Tonic contraction (sphincters)

Question 2

What is the function of the small intestine?

Answer 2

Location for almost all digestion and absorption

Secretion of Chyme into the colon

Question 3

What types of motility are in the small intestine during the fed state?

Answer 3

Segmentation
Peristalsis
(these types are rhythmic phasic contractions (RPCs))

Question 4

How does segmentation work?

Answer 4

Rings of contractile muscle at intervals contract then relax pushing bolus around.

Used for mixing mainly

Question 5

How does peristalsis work?

Answer 5

Sequential contractions of rings of circular muscle followed by sequential relaxation.

Combination of activity between muscular layers, with sequential activity in each of them.

Propels chyme along

Question 6

What regulates peristalsis during the fasting state?

Answer 6

Migratory motor complex (MMC).

Question 7

What is the MMC?

Answer 7

Large sweeps of electrical activity causing contraction down the small intestine.

Question 8

What is the purpose of the MMC?

Answer 8

Propel particles from the stomach into the duodenum
Clear small intestine of its residual content (undigested food)
Stops colonic bacteria from entering into the terminal ileum

Question 9

What types of reflex are present in the ileum?

Answer 9

Ileogastric reflex
Gastroileal reflex

Mediated via the ENS

Question 10

What is the Ileocaecal Sphincter?

Answer 10

Separates the ileum from the colon.

Operate based on sensory neurones detecting pressure changes via the ENS.

Question 11

What is the Colon?

Answer 11

Last 4ft of the GIT
Surface area only 1/30th of the small intestine.
No villi

Question 12

What are the parts of the colon?

Answer 12

Ascending
Transverse
Descending
Sigmoid
Rectum

Question 13

What are Taeniae Coli?

Answer 13

Longitudinal muscle layers thickened to form 3 muscular bands which run the length of the colon

Question 14

What is the function of the Colon?

Answer 14

Absorb large quantities of fluid and electrolytes thus converting liquid content to solid.

Metabolises fibres into short chain fatty acid (glutarate) to be absorbed. (caused by microbiota fermenting the fibres into the SCFA)

Storage and reservoir function

Regulate release of faecal material

Provides environment for comensal bacteria which synthesise vitamins

Secretes mucous and ions.

Question 15

What are the functions of the proximal colon?

Answer 15

site of absorption and bacterial fermentation

Question 16

What are the functions of the distal colon?

Answer 16

reservoir/storage function

Question 17

What do Colonic rhythmic phasic contractions do?

Answer 17

cause slow net distal propulsion with extensive mixing/turning over

Short duration - contractions have no propagation and varying amplitudes

Long duration - contractions over short distances which turn over and propel the semi-solid to solid contents more effectively

Question 18

What is Colonic giant migrating contractions?

Answer 18

Colonic motility:

GMCs are large amplitude lumen occluding contractions over entire colon that precede defecation.

Question 19

How is motility stimulated in the colon?

Answer 19

When something is taken (food) resulting in distention and therefore stimulation of motility.

Question 20

What are some western diseases and what causes them?

Answer 20

Constipation 
Diverticular disease
Haemorrhoids 
Polyps 
Cancer of colon
Irritable colon 
Ulcerative colitis 
Caused by populations which have a low fibre diet

Question 21

What is a laxative?

Answer 21

Something which stimulates motility

Question 22

What are the classifications of laxatives?

Answer 22

Osmotic laxatives
Bulk laxatives
Stimulant laxatives
Faecal laxatives

Question 23

What part of the colon is innervated by which nerve?

Answer 23

Vagus - innervates ascending and transverse

Pelvic - innervates descending and rectum

Question 24

What does stimulation of the pelvic nerve bring about?

Answer 24

Causes expulsive movement (GMCs) of the distal colon and sustained contraction of some segments.

Question 25

What is the process of the defaecation reflex?

Answer 25

1. distention of the rectum. 2. stimulation of stretch receptors 3. stimulation of myenteric plexus. 4. stimulates motility and peristalsis. 5. reinforcement in the form of a parasympathetic defaecation reflex 6. mediated by via the sacral segments of the spinal cord 7. results in amplification of peristaltic waves and relaxation of the internal anal sphincter. 8. defaecation can be inhibited by conscious control over the external anal sphincter

Question 26

What are the functions that motility has in the small intestine?

Answer 26

Mixing - chyme from stomach with secretions of pancreas, liver and intestines Propulsion - Moving food to the correct sites for digestion, absorption and make way for further material to be emptied from stomach Release of Chyme into the colon

Question 27

What regulates ileal flow into the colon through the Ileocaecal Sphincter

Answer 27

Luminal contents and pressure both proximal and distal to the sphincter. Distention of the ileum = relaxation of the sphincter Distention of the proximal colon = contraction of the sphincter

Question 28

What are the phases of MMC movement?

Answer 28

1. A prolonged quiescent period 2. Period of increasing action-potential frequency and contractility 3. Period of peak electrical and mechanical activity that lasts a few minutes, 4. Period of declining activity that merges into the next quiescent period.

Question 29

What are the types of motility in the Colon?

Answer 29

1. Colonic Rhythmic Phasic Contractions | 2. Giant Migrating Contractions

Question 30

What are bulk laxatives?

Answer 30

- Indigestible material passes quickly activating pressure receptors which initiate the Myenteric plexus

Question 31

What are osmotic (saline) laxatives?

Answer 31

- create a hyperosmotic environment in the colon drawing water into the colon (eg. lactulose)

Question 32

What are Faecal laxatives?

Answer 32

- stimulate defecation (eg. docusate)

Question 33

What are stimulant laxatives?

Answer 33

-stimulate the ENS directly to cause motility (eg. senna danthron)

Question 34

What is the ileogastric reflex?

Answer 34

- ileal distention leads to decreased gastric motility (inhibitory reflex)

Question 35

What is the Gastroileal reflex?

Answer 35

- increased gastric activity causing increased ileal motility and increased movement of chyme through the ileoceacal valve (excitatory reflex)