Intestinal motility Flashcards
What are the 3 patterns of motility?
Peristalsis
Segmentation
Tonic contraction
What is segmentation in intestinal motility?
Non-propulsive movement.
Mainly for mixing of chyme with secretions of pancreas, liver and intestines.
Enhances the digestion and absorption of dietary nutrients.
Phasic contractions.
How does the intestine act as a reservoir?
Holds content so undigested material does not just pass through - chyme is digested.
Made possible by sphincters.
This is tonic contractions.
What is peristalsis in intestinal motility?
Used for propulsion - moves food and digestive products towards the anus.
Results in elimination of nondigested, non-absorbed material.
Phasic contractions.
What is segmentation in the fed state?
Rings of circular muscle at intervals contract and then relax.
Then adjacent rings contract and relax.
This causes mixing.
What is peristalsis in the fed state?
Sequential contractions of rings of circular muscle followed by sequential relaxation.
The circular muscles contract behind the food.
The longitudinal muscles contract ahead of the food.
Then contraction of circular muscles forces the chyme forwards.
What is the MMC?
In the fasting state the small bowel is quite empty.
It exhibits synchronised, rhythmic changes in both electrical and motor activity - the Migrating Motor Complex.
This is for nutritional and cleansing functions.
What are the phases of the Migrating Motor Complex?
A prolonged quiescent period.
Period of increasing action potential frequency and contractility.
Period of peak electrical and mechanical activity that lasts a few minutes.
Period of declining activity that merges into the next quiescent period.
What is the role of the MMC?
Propels particles greater than 2mm from the stomach into the duodenum.
It also clears the small intestine of residual content - undigested food, desquamated cells, and intestinal and pancreatic biliary secretions.
It stops colonic bacteria migrating into the terminal ileum.
When does MMC occur?
MMCs originate in the stomach and travel to the distal end of the ileum.
Feeding terminates MMC and initiates the appearance of the ‘fed motor pattern segmentation and peristalsis.
The ENS, humoral factors and extrinsic innervations all regulate MMCs and the fed state.
How does motilin impact the MMC?
Motilin is a hormone synthesised in the duodenal mucosa and released just before the initiation of phase 3 of the MMC cycle.
Motilin is a 22 amino acid peptide.
What is the colon?
The last 4ft of the GIT.
It has no villi.
What are the functions of the colon?
Absorbs liquid, for recycling
Absorbs short chain fatty acids
Regulates release of faecal matter.
Store and reservoir of faecal matter.
Provides environment for synthesis of vitamins B complex and K-beneficial bacteria.
Secretes mucous and ions.
What are the regions of the colon?
Proximal colon: Caecum and Ascending colon - site of absorption and bacterial fermentation.
Transverse colon
Distal colon: Descending colon and Sigmoid colon - for storage.
What is colon motility?
Rhythmic phasic contractions
Giant migrating contractions.
What are rhythmic phasic contractions?
Or haustral contractions.
Segmentation - in ascending and transverse colon
This increases contact of the faeces with mucosal walls so there is reabsorption of fluids, electrolytes and vitamins.
The contraction causes pouches ‘Haustra’.
What are giant migrating contractions?
Propulsion - in transverse and descending colon.
To release faecal matter.
These are bigger contractions.
When does giant migrating contractions occur?
During both fasting and postprandial states (just after eating)
Occurs randomly about 2-10 times a day.
What is Hirschsprung disease?
Or Aganglionic megacolon.
There is no ganglia so there is no stimulation for propulsion of the faecal stream above the point where the nerves are missing and hypertrophy of the normal proximal colon.
What are long-range intestinal reflexes?
Food in the stomach can send signals to the colon to contract.
There are also signals from the small intestine to activate contraction in the large intestine.
This is important for regulation of colon motility.
How do faeces regulate colon motility?
Left over chyme leaves duodenum then enters the colon, and causes distention.
This activates the stress reflex, activates stress receptors.
Signals to myenteric nerve plexus, and triggers the haustral contractions.
What is the gastrocolic reflex?
Increased motility of the colon due to the stretch of the stomach.
How does the fundus cause regulation of colon motility?
Distention in the fundus of the stomach causes G cells to secrete gastrin.
Gastrin the triggers mass movement in the colon.
How does the pylorus cause regulation of colon motility?
Distention of the pylorus causes acetylcholine to be secreted.
The Ach signals the parasympathetic nervous system, which increases colon motility.
