Gastrointestinal Motility Flashcards
Mixing movements
local constrictive contractions (segmentation) and peristaltic contractions
Propulsive Movements
Peristalsis moves contents down the GI tract
What is the stimuli for peristalsis
Distention (stretch receptors)
Migrating Motor Complex MMC
strong wave of contractile activity that spreads down through the GI BETWEEN MEALS.
Once every 2 hours in the FASTED STATE
sweeps clean the GI lumen by allowing undigested materials >2 mm to move out of the stomach and through the small intestine.
Control of contractive activities in the GI tract
- ) CNS
- )ENS
- ) Electrical coupling between cells
- ) Hormal factors
Role of the inner circular layer
makes sections of the gut longer and thinner
Role of the outer longitudinal layer
makes sections of the gut shorter and wider
CNS control of contractive activities
coordination
PNS = increased motility SNS= decreased motility
ENS control of ocntractile activities
local movements
“Law of the Gut”
role of electrical coupling in control of contractile activities
spread of contraction wave associated with BER
role of hormones and humoral factors in control of contractive activity
stimulate and inhibit motility
Gastrin
Released in response to food in the stomach
Increases stomach motility (increases force of stomach contractions ) –> promote emptying
Motilin
initiates MMC
Cholecytsokinin
secreted by I cells (duodenum, and jejunum) in response to fatty acids, amino acid
Decreases gastric motility and increases gallbladder contract-ability
Secretin
Released by S cells (located in the duodenum) in response to acid
Decreases motility of most of the GI tract
Gastric Inhibitory Peptide (GIP)
Secreted by K-cells (duodenum and jejunum) in response to fatty acids, amino acids, and oral glucose
Mildly Decreases gastric motility
Muscle distribution of the esophagus
Upper = skeletal Middle = mixed Lower= smooth
Primary vs secondary peristalsis of the esophagus
Primary - Vagus nerve. Peristaltic wave contines at UES
Secondary - occurs due to continued distention of the esophagus if the primary wave did not completely clear the bolus (Does not require vagus nerve- stretch receptors detect distention)
Tonically contracted LES
Both parasympathetic and sympathetic nerve stimulation cause contraction of LES .
ENS aline can maintain constriction
LES relaxation
primarily mediated by vagovagal reflex -causes relaxation of the circular muscle layer
Achalasia
LES does not fully relax during swallowing
Degeneration of ganglions in myenteric plexus often due to autoimmune attack
Primary Function of LES
Prevent reflux of gastric contents back into the esophagus
in a normal person LES pressure is ALWAYS higher than gastric pressure EXEPT during swallowing
Functions of the stomach
reservoir for ingetsted food
production of chyme
control rate of emptying of gastric contents into the duodenum
Fundus
superior portion of the stomach
Body of the stomach
reservoir area
Antrum of the stomach
more muscular- controls the rate or chyme efflux
Pyloric Sphincer
normally tonally constricted- allows fluid and small particles (<2mm) to pass but prevents most of the chyme from entering the duodenum even in the presence of strong contractions
Regulation of gastric emptying
Neural and humoral mechanisms
Which hormone causes relaxation of the orad stomach
CCK - I cells release CCK that acts on vagal afferent to cause relaxation (VIP, NO) of the stomach
Vomitting
GI irritation causes paracrine release of serotonin 5-HT from enterochromaffin cells which stimulate vagal afferents to the vomitting center
which cells in the GI tract release serratonin (what kind of release?)
Enterochromafin cells - paracrine release
Which cells in the GI tract release histamine
Enterochromafil Like cells
Receptors that deal with vomiting (drugs that are antagonists for that receptor)
5-HT3 receptos: Ondansetron
B2 receptors: Metroclopramide
H2 receptors: Diphenhyramine
what causes the stomach to fill in the vomiting response?
intrathorasic pressure falls and intra-abdominal pressure rises (stomach fills and pushes contents up to esophagus)
Gastroenteroc reflex
tissues are mad more excitable by the distention of the stomach and the entry of chyme into the duodenum
Intestinoepithelial reflex
overstistention of one segment will cause reflex relaxation of the rest if the intestine
Gastroileal Reflex
increased activity in the stomach will increase motility in the illeum and accelerate the movement of chyme through the ileocecal sphincter
Gastrocolic reflex
gastric distention increases activity in the colon
Function of the ileocecal valve
prevent reflux of colonic contents into the intestine
Distention of terminal ileum causes relaxation
Distention of cecum causes contraction
Gastrin and gastroileal reflex relax the valve
Mass Movement
propulsive peristaltic waves. Occur about 1-3 times per day (commonly following meal times)
which reflexes increase mass movement activity
gastrocolic and duodenocolic refelxes
affect of gastroileal reflex on the ileocecal valve
relax
affect of gastrn on ileocacal valve
relax
Rectosphinteric reflex (defacation)
mass movement from the sigmoid colon fills the rectum which then contracts
relax internal anal sphincter
contract external anal sphincter (normally relaxed at rest)
Borborygmi
noise made by the movement of gas through the intestines due to peristalsis. Can be generated by MMC and mass movements
