GI Motility Flashcards
What three functions does motor activity of the GI tract allow?
- Segmented contractions which allow for the churning and mixing of food with no propulsive movements.
- Peristaltic contractions - Propagated movement of food in the caudal direction. This eliminates non-digested and nonabsorbed food.
- Allows for hollow organs such as the stomach and the intestines to act as reservoirs with the help of the sphincters.
What two muscle type are important for the motor activities in the GI tract?
Tonic and Phasic muscle
Structure of the small intestine?
9ft long extending from the stomach to the colon. Has enterocytes which line the villi and stem cells present in the crypts.
Where does majority of absorption occur?
Within the small intestines
Functions of the small intestines?
Digestion, Absorption, Secretion and motility.
What are the functions of motility in the small intestines?
- Mixes chyme with secretion from the pancreas, liver and intestines.
- Propulsion - Moves food to correct site of absorption
- Releases chyme into the colon
What types of motility are experienced in the absorptive state?
Segmentation - Rings of circular muscle at intervals contract then relax followed by the rings of adjacent circular muscle with the overall result of mixing.
Peristalsis - Sequential contraction of rings circular muscle followed by relaxation. main result is to propel chyme along.
During the fasted state, is there still motility?
Yes, there is the migrating motor complex
What is the migrating motor complex (MMC)
It is a distinct pattern of electromechanical activity in the GI tract that is undergone during the fasted state.
What it the purpose of MMC?
It is to eliminate any undigested materials from the stomach.
What are the phases of MMC
- Prolonged period of quiescence;
- Increased frequency of action potentials and smooth muscle contractility.
- Few minutes of peak electrical and mechanical activity, and;
- Declining activity which merges with Phase 1
What stops MMC?
Feeding as it initiates segmentational and peristaltic contractions
what regulates the transition from MMC to fedstate?
The enteric nervous system, Humoral factors and extrinsic innervations
What hormone is the major determinant of MMC?
Motilin
release just before phase 3.
Synthesised in duodenal mucosa.
What controls smooth muscle contractility?
ACH, somatostatin and motilin - contraction
Vasoactive intestinal peptide - Relaxation.
Stretch cause contraction mediated by ca2+ influx
ENS mediated by ANS.
what is the ileogastric reflex?
inhibition of gastric motility due to distension of the ileum.
What is the Gastroileal reflex?
It is increased ileal motility caused by the increased gastric activity. leading to the movement of chyme through the ileoceacal valve.
What is the ileoceacal valve?
Sphincter that separates small intestine from large intestine.
Functions of the colon?
Absorbs large quantities of fluid and electrolytes, forming solids.
Absorbs SCFAs
Storage
Regulates release of faecal matter
Provides ideal environment for vitamin synthesis
Secretes mucous and ions.
What are the two distinct regions of the colon
Proximal colon and distal colon
What are the two major types of colonic motility?
Rhythmic phasic contractions.
Giant migrating contractions
What diseases are caused by a western diet?
Constipation, Diverticular disease haemorrhoids polyps cancer of the colon irritable colon ulcerative colitis
How do stimulant laxatives work?
By increasing motility through the activation of chemoreceptors and the myenteric plexus.
How do saline laxatives work?
By drawing water into the bowel via osmosis due to high concentration of osmotic substances
How do emollient laxatives?
By increasing intestinal fluid
How do bulk forming laxative work?
These are non-fermentable so they cause swelling due to water absorption which cause distention and motility.
How is motility in the colon controlled?
By the autonomic nervous system. Sympathetic activation inhibits colon motility while parasympathetic increases motility.
