Motility of the GI Tract Flashcards
What is motility in terms of the GI tract?
contraction and relaxation of the wall and sphincters of the GI tract, rate regulated
What is the role of the muscularis propria? What muscles play a role?
Smooth muscles that mix and circulate content of the lumen and propel through the GI tract
Circular muscle changes diameter and longitudinal muscle changes length
Are slow waves APs?
No they are depolarization and depolarization of the membrane
How does the number of APs on a slow wave effect contractions?
The greater number of APs causes a larger contraction
What stimulates slow waves?
Stretch
Ach
Parasympathetics
What decreases slow waves?
NE and sympathetics
What are phase contractions? Where do they occur?
periodic contractions followed by relaxation
esophagus, stomach (antrum), SI, and all tissue involved in mixing and propulsion
What are tonic contractions? Where do they occur?
maintain a constant level of contraction without regular periods of relaxation
orad of stomach, lower esophageal, ileocecal, and internal anal sphincters
Where is the submucosal plexus of the enteric nervous system found? What does it control?
plexus in submucosa
GI secretions and local blood flow
Where is the myenteric plexus found? What does it control?
between longitudinal and circular layers
GI movements
What cells are the pacemaker of GI smooth muscle?
Interstitial cells of Cajal (ICCs)
What allows ICCs to spread and propagate slow waves?
gap junctions
electrical activity= freq of contractions
Which phases of swallowing are voluntary and which are involuntary?
Voluntary= oral phase
Involuntary= pharyngeal and esophageal
What happens during the pharyngeal phase of swallowing?
soft palate pulled up –> epiglottis moves –> UES relaxes –> peristaltic wave of contractions initiated in pharynx –> food propelled through open UES
What controls the esophageal phase of swallowing?
Swallowing reflex and enteric nervous system
What are primary peristaltic waves of the esophageal phase? Can they occur after vagotomy?
continuation of pharyngeal peristalsis, controlled by medulla
NO
When do secondary peristaltic waves occur? Can they occur after vagotomy?
if primary wave fails to empty esophagus or if gastric contents reflux into esophagus
Can occur in absence of oral and pharyngeal phases and after vagotomy
What are the steps of the swallowing reflex?
food in pharynx –> afferent sensory input via vagus/glossopharyngeal –> swallowing center in medulla –> brainstem nuclei –> efferent input to pharynx
What three parts have high pressure contractions before swallowing?
UES
LES
esophagus
Why is intrathoracic pressure an issue? How does out body help with this?
need to keep air and gastric contents out
UES and LES closed except when food bolus is passing from pharynx to esophagus or esophagus to stomach
What is achlasia?
impaired peristalsis and incomplete LES relaxation during swallowing –> elevation of LES resting pressure
Results in backflow of food in the throat (regurgitation), difficulty in swallowing (dysphagia), heart burn, chest pain
What are causes of achlasia?
Decreased number of ganglion cells in myenteric plexuses
Degeneration preferentially involves inhibitory neurons producing NO/VIP
Damage to nerves in the esophagus preventing it from squeezing food into stomach
What is GERD?
changes in barrier between esophagus and stomach (LES relaxes abnormally or weakens) causing low pressure in LES
What is the job of the orad region of the stomach?
Receptive relaxation= decrease pressure and increase volume, caused by vagovagal reflex
Minimal contractions aka little food mixing
What effect does CCK have on the orad region?
decrease contractions and increase gastric distensibility
What is the primary event of the caudad region of the stomach? Where is it the strongest?
Peristaltic contraction (mid stomach to pylorus)
Increase in force and velocity as approach pylorus
What is retropulsion?
Propulsion of gastric contents back into the stomach for further mixing and reduction of particle size
What increases forces of contractions and APs?
parasympathetics
gastrin
motilin
What decreases APs and force of contractions?
sympathetics
secretin
GIP
What increases gastric emptying?
decrease in distensibility of the orad
increase peristaltic contractions of caudad
decrease tone of pylorus
increased diameter
inhibition of segmenting contractions of proximal duo
What decrease gastric emptying?
relaxation of orad (increase in distensibility)
decrease force of peristaltic contractions
increase tone in pyloric sphincter
segmentation contraction in intestine
What is the entero-gastric reflex? What stimulates it?
Neg feedback from duo slows down rate of gastric emptying, hormone dependent
Acid in duodenum= secretin –> gastrin inhibition
Fats in duodenum= stimulate CCK and GIP
Hypertonicity in duodenum= inhibit emptying
What can cause slow gastric emptying? How can it be treated?
gastric ulcer, cancer, eating disorder, vagotomy
pyloroplasty, balloon dilation
What is gastroparesis? What are the symptoms?
Slow emptying of stomach/paralysis of stomach in absence of mechanical obstruction, DM common cause, injury to vagus
Nausea, vomiting, early feeling of fullness when eating, weight loss, abdominal bloating, abdominal discomfort
What happens when we fast? Why is this important?
Myoelectric complex/migrating motor complex
Periodic burst of peristaltic contractions mediated by motilin
Cleansing mechanisms to prevent small intestinal bacterial overgrowth which can lead to small bowel motility nausea anorexia and bloating
What are segment contractions of the SI?
generate back and forth movements, produce no forward, propulsive movements
What are peristaltic contractions of the SI?
circular and longitudinal muscles work in opposition to complement each other, reciprocally innervated
Do slow waves initiate contractions in the SI?
NO
APs/spike potentials necessary for muscle contraction to occur
slow wave frequency sets max frequency of contractions
(duo (12)»_space; jeju (10)»_space; ileum (8) )
What happens when the SI becomes distended?
Signals for the release of serotonin by enterochromaffin cells which bind to receptors in IPANs initiating peristaltic reflex
What stimulates contraction in the SI?
serotonin, prostaglandins, gastrin, CCK, motilin, and insulin
What inhibits contraction in the SI?
epi, secretin, and glucagon
What is the role of the myenteric and meissner/submucosal plexus in the SI?
myenteric= regulate relegation and contraction of intestinal wall
meissner= sense lumen enviorment
What are the steps of the vomiting reflex?
Reverse peristalsis in small intestine –> stomach and pylorus relaxation –> forced inspiration to increase abdominal pressure –> movement of larynx –> LES relaxation –> glottis closes –> forceful expulsion of gastric contents
What coordinates the vomiting reflex?
medulla, nerve impulses transmitted by vagus and symp afferents to brain stem nuclei
What allows the flow of contents from the SI into the LI?
Ileocecal junction
Distention of ileum cause relaxation of sphincter allowing for flow of contents from ileum into colon
Distention of colon causes contraction of sphincter preventing passage
What muscles layers are found in the LI?
circular which is continuous from cecum to the anal canal
longitudinal= taeniae coli of 3 flats bands of longitudinal fibers that run from cecum to rectum
What sphincters are found in the LI?
internal anal of smooth muscle and external of striated muscle
What are haustras?
small pouches that give LI segmented appearance, not fixed
What is the parasympathetic innervation of the LI?
Vagus for cecum ascending and transverse colon, pelvic nerves for sacral portion of spinal cord (S2-4), descending and sigmoid colon, rectum
What is the sympathetic innervation of the LI?
(T10-L2)= superior mesenteric ganglion for proximal regions, inferior mesenteric ganglion for distal, and hypogastric plexus for distal rectum and anal canal
What innervates the external anal sphincter?
Somatic pudendal nerve
What are mass movements?
Occur in colon over large distances 1-3 times a day stimulating defecation reflex, final movement propels fecal content into the rectum
What happens when the anal canal fills?
smooth muscle wall of the rectum contracts and internal sphincter relaxes= rectosphincteric reflex
What controls the rectosphinteric reflex?
partially by ENS, reflex reinforced by activity of neurons within the spinal cord
What happens in Hirschsprung’s disease?
ganglion cells absent from segment of colon –> VIP low –> SM constricts and loss of coordinated movements –> colon contents accumulate
cause difficulty in passing stool (congenital megacolon), failure to pass meconium, poor feeding, jaundice, vomiting
What is the vago-vagal reflex?
long reflex, generally stimulatory –> increase motility secretomotor vasodilatory activities, vagus carries both aff and eff
What is the intestino-intestinal reflex?
depends on extrinsic neural connections, inhibitory, if bowel grossly distended, contractile activity in rest of bowel inhibited
What is the gastroileal reflex?
gastric distention relaxes ileocecal sphincter
What is the gastro-duo-colic reflex?
distention of stomach/duo initiates mass movements, transmitted by ANS
