GI Motility class Flashcards
What do circular muscle contractions decrease?
diameter of the segment
What do longitudinal muscle contractions decrease?
the length of the segment
Esophagus, stomach (antrum), small intestine and all tissues involved in mixing and propulsion have what type of muscle contractions?
phasic
What are slow waves?
are depolarization and repolarization of the membrane potential
originates in the interstitial cells of Cajal
NE (increases/decreases) the amplitude of slow waves
decreases
Where is the swallowing center located?
in the medulla
Food in the mouth is detected by somatosensory receptors near ______
the pharynx
Afferent info from the mouth is carried to the medulla via what nerves during the swallowing reflux?
vagus and glossopharyngeal nerves
In the circuit involved in the swallowing reflex, what do the efferent signals connect to?
input to striated m of the pharynx and upper esophagus
*Food in pharynx-> afferent sensory input via vagus/gloss->swallowing center (medulla)->brain stem nuclei->efferent input to pharynx
Describe the oral phase during swallowing
the only voluntary phase
striated m
tongue forcing bolus towards pharynx which contains high density of somatosensory receptors
What receptors initiate the involuntary swallowing reflux in the medulla?
somatosensory receptors
Is the pharyngeal phase voluntary or involuntary? what type of muscle is involved?
involuntary
straited m - pharynx and upper part of esophagus
What are the actions during pharyngeal phase?
Passage of food through pharynx into esophagus
soft palate rises and closes of nasopharynx
epiglottis covers opening of larynx
UES relaxes
Swallowing reflex inhibits respiratory center
ends with peristaltic wave initiated in pharynx
The esophageal phase is controlled by what 2 things?
swallowing reflex - responsible for closing UES
and ENS
During the esophageal phase, there are two types of peristaltic waves. Describe the primary peristaltic wave
Continuation of pharyngeal peristalsis
controlled by medulla
CANNOT occur after vagotomy
During the esophageal phase, there are two types of peristaltic waves. Describe the secondary peristaltic wave
Occurs if primary contraction fails to empty the esophagus or when gastric contents reflux into the esophagus
induced by distention
repeats until bolus gone
Swallowing center and ENS involved
Can happen in absence of oral and pharyngeal phases and after vagotomy
Mid and lower esophagus consists of _____ muscle and are strongly controlled by what?
smooth
vagus nerves that act through the myenteric nervous system
If vagus nerve is cut, how can secondary peristaltic waves occur?
myenteric plexus becomes excitable enough after several days to cause 2ndary waves
When does gastroesophageal reflux occur?
when intra-abdominal pressure is increased
seen in obesity and pregnancy
What three parts of the upper GI tract are above atmospheric pressure and why?
UES and LES - High pressure because they are closed
Below the diaphragm (pressures in the body of the esophagus are similar to those within the body cavity in which the esophagus lies)
Fundus - because there is some contraction
The intrathoracic location of the esophagus poses a challenge. Keeping air out of the esophagus at the upper end and keeping acidic gastric contents out of the lower end. How are the problems solved?
both UES and LES are closed, except when food bolus is passing from pharynx to esophagus to stomach
The opening of the LES is mediated by what?
peptidergic fibers of the vagal nerve
How does the vagal input on the LES relax the sphincter?
release of vasointestinal peptide (VIP)
Role of nitric oxide (NO) a neurotransmitter involved in relaxation of LES has been proposed
Gastroesphageal reflux disease (GERD) happens in 1/10 people. What happens with GERD and what are some symptoms?
Abnormal relaxation of LES
Backwash of acid, pepsin, and bile into esophagus
Heartburn, chest pain, dysphagia, acid reflux,
What can GERD lead to?
stricture of esophagus
Asthma
Chronic sinus infection
Barrett’s esophagus
What is achalasia?
Impaired peristalsis
Lack of LES relaxation during swallowing and back up of food
Causes: lack of VIP or enteric system has been knocked out
Elevation of LES resting pressure
Damage to nerves maybe due to immune system
WEIGHT LOSS occurs!
What happens during receptive relaxation in the orad region of the stomach?
to receive the food bolus in the stomach the pressure decreases and the volume of the orad region increases
Vagovagal reflux
Describe the activity in the orad region of the stomach
Minimal contractile activity
little mixing of ingested food
CCK decreases contractions and increase gastric distensibility
In what region of the stomach is most of the mixing and digestion of food is taking place?
caudad region
What happens during the primary contractile even in the caudad region of the stomach?
From mid stomach to pylorus there are peristaltic contractions. as the contractions approach the pylorus, they increase in both force and velocity (max freq 3-5 w/m)
the phase lag decreases as the wave approaches the antrum
the wave of contraction closes the pylorus and gastric contents are propelled back to stomach (retropulsion)
What is the effect of parasympathetic and sympathetic stimulation on gastric contractions during mixing and digestion of food? WHat other hormones have the same effects?
PS - via vagus, increases AP and force of contractions
Gastrin and motilin - similar to PS
SP - decreases AP and force
Secretin and GIP
What is the rate of gastric emptying increased by?
decrease distensibility of the orad
increase force of peristaltic contractions of caudad stomach
decrease tone of pylorus
increase diameter and inhibition of segmenting contraction of prox duodenum
How long does gastric emptying take?
3 hours
Why is gastric emptying closely regulated?
to provide adequate time for neutralization of gastric H in the duodenum and sufficient time for digestion and absorption
receptors lie in small intestines
What are factors that inhibit gastric emptying?
relaxation or orad
decrease force of peristaltic contractions
increase tone of pyloric sphincter
segmentation contractions in intestine
Info from the duodenal receptors to the gastric sm m is carried by neurons of what?
submocosal and myenteric plexuses - respond to physical and chemical properties
What are H+ inhibitory effects mediated by?
intrinsic neural reflex involving interneurons in the myenteric plexus
What is gastroparesis?
Slow emptying of stomach/paralysis of stomach
20% of type 1 diabetics
Damage to vagus n. - idiopathic and HBG
Symptoms fullness, weight loss, nausea, vomiting
Large particle of undigested residue remaining in stomach are emptied by what?
migrating myoelectric complexes
motilin
90 min intervals
feeding inhibits MMCs
Absence of MMCs in stomach have been associated with what?
gastroparesis
Segmentation contractions serve to…..
mix the chyme and expose it to pancreatic enzyme and secretions
produces no forward, propulsive movement along small intestine (back and forth)
Peristaltic contractions serve to ….
propel the chyme towards the large intestines
How do peristaltic contractions work?
Behind bolus: circular m contracts and longitudinal m relaxes
In front: circular m relaxes and longitudinal m contracts
work in opposition
are reciprocally innervated
Slow waves in stomach can induce a weak contraction. slow waves in the intestines ….
DO NOT initiate contractions and spike potentials (AP) are necessary for muscle contractions to occur
Slow wave freq sets max freq of contractions
There is a gradient in the maximal frequency of the contractions along the SI. What are the slow wave freqs?
duodenum - 12 c/m
jejunum - 10 cycles/m
ileum - 8 c/m
Decrease in freq towards the ileocecal junction
From the stomach, what is released to initiate the peristaltic reflex in SI?
serotonin (5-HT) is released by ECCs and binds to receptors in IPANs which then initiate the relfex
What hormones can stimulate contractions in the SI?
serotonin (stored in large quantities in small bowel) Certain PGs Gastrin CCK motilin insulin
What hormones can inhibit contractions in the SI?
epinephrine, released from adrenal glands
secretin
glucagon
What coordinates the vomit reflex?
medulla
vagal and sympathetic afferent nerve fibers
What are the order of events of vomiting reflex?
reverse peristalsis in SI relaxation of stomach and pylorus forced inspiration to increase abdominal pressure movement of larynx relaxation of LES closure of glottis forceful expulsion
What allows flow of contents from ileum into colon?
distention of ileum causes relaxation of sphincter
What prevents passage of contents from colon to ileum ?
distention of colon causes contraction of sphincter
What are the main functions of lg intestine?
absorption of water and vitamins and conversion of digested food into feces
Where is the ENS of the lg intestine concentrated?
beneath teneae
What is the PNS of the colon?
vagus nerve and pelvic nerves
What is the SNS of the colon?
SMG, IMG,
hypogastric plexus: distal rectum and anal canal
Somatic pudendal nerves: external anal sphincter
What are the major excitatory mediators?
ACh and substance P
What are the major inhibitory mediators?
VIP and NO
Where does segmentation contractions occur in lg intestine?
cecum and ascending colon
appear, disappear, and form again at another location w/i lg intestine
What do mass movements do in lg intestines?
move content over long distances and stimulate defecation reflex
What does poor motility of lg intestine cause?
greater absorption and hard feces in transverse colon and cause constipation
Rectum is usually (full/empty)
empty
Frequency of segmentation contractions in rectum’s upper region (greater than\less than) sigmoid colon
greater than
What is the rectosphincteric reflex?
as rectum fills, sm m wall of rectum contracts and internal anal sphincter relaxes
Controlled partly by ENS
Reinforced by neurons in spinal cord
Why does the rectosphincteric reflux not result in defecation?
voluntary external anal sphincter by puborectalis m
What is the gastroileal reflex?
(gastroenteric)
gastric distention relaxes ileocecal spincter
What is the gastro and duodeno-colic reflexes?
distention of stomach/duodenum initiates mass movments (ANS)
What type of reflex is the ileocelcal sphincter?
intestino-intestinal reflex (short reflex)
generally inhbitory
involving only ENS
What is hirschsprung disease?
megacolon
ganglion cells absent
VIP levels low - Sm m contstriction, loss of coordinated movement
Present at birth
No bowel movment
Jaundice, vomit, poor feeding, swollen belly
Tx: remove colon w/o ganglia
What is diverticular disease?
small sacs of intestinal lining that bulge outward at weak spots
excess pressure in colon
Can occur anywhere in colon (descending colon)
If diverticulum becomes infected = diverticulitis
Symp: abdominal pain, swelling, bloating, diarrhea
Increases with age (about 50% > 60 and ~100% > 80)
Tx: dietary and lifestyle interventions
