Gastrointestinal Motility Flashcards by Jordyn Schumacher

Mixing movements

local constrictive contractions (segmentation) and peristaltic contractions

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Propulsive Movements

Peristalsis moves contents down the GI tract

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What is the stimuli for peristalsis

Distention (stretch receptors)

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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.

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Control of contractive activities in the GI tract

) CNS
)ENS
) Electrical coupling between cells
) Hormal factors

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Role of the inner circular layer

makes sections of the gut longer and thinner

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Role of the outer longitudinal layer

makes sections of the gut shorter and wider

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CNS control of contractive activities

coordination

PNS = increased motility 
SNS= decreased motility

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ENS control of ocntractile activities

local movements

“Law of the Gut”

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role of electrical coupling in control of contractile activities

spread of contraction wave associated with BER

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role of hormones and humoral factors in control of contractive activity

stimulate and inhibit motility

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Gastrin

Released in response to food in the stomach

Increases stomach motility (increases force of stomach contractions ) –> promote emptying

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Motilin

initiates MMC

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Cholecytsokinin

secreted by I cells (duodenum, and jejunum) in response to fatty acids, amino acid

Decreases gastric motility and increases gallbladder contract-ability

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Secretin

Released by S cells (located in the duodenum) in response to acid

Decreases motility of most of the GI tract

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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

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Muscle distribution of the esophagus

Upper = skeletal 
Middle = mixed 
Lower= smooth

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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)

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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