Motility Of GI Tract - Lopez Flashcards
When circular muscle contracts what happens?
Diameter decreases
When longitudinal muscle contracts what happens?
Length of segment decreases
Describe phasic contractions
Periodic contraction, followed by relaxation
What body parts use phasic contraction?
Esophagus, stomach (antrum), small intestine
ESS
Describe tonic contractions
Constant level of contraction, no relaxation
What body parts use tonic contractions?
Stomach (orad), lower esophagus, ileocecal, internal anal sphincters
SLEii
What are slow waves a unique feature of?
What are they not?
Smooth muscle
Action Potential
TRUE or FALSE: Subthreshold depolarization can produce contractions in GI smooth m.?
TRUE, but weak
Aka basal contractions
What neurotransmitter increases the amplitude of slow waves and # of APs?
Decreases?
ACh
NE
What else increases amplitude of slow waves and # of APs?
What else decreases?
Stretch, PS
Sympathetics
Where do slow waves originate?
Interstitial cells of Cajal (ICC)
How do slow waves spread through ICC to smooth m.?
Gap junctions
What are the 3 phases of swallowing and which are voluntary/involuntary?
Oral (V)
Pharyngeal (IV)
Esophageal (IV)
Describe the pharyngeal phase of swallowing
Soft palate pulled up -> epiglotis movies -> UES relaxes -> peristaltic wave initiated -> food propelled through open UES
What controls the esophageal phase of swallowing?
Swallowing reflex and ENS
Where is the swallowing center located?
Medulla
What nerves sense food in the pharynx?
Vagus and glossopharyngeal
What inhibits the respiratory center during the pharyngeal stage of swallowing?
Swallowing center
Describe the primary peristaltic wave
Continuation of pharyngeal peristalsis
Cannot occur after vagotomy
What does the secondary peristaltic wave do?
Occurs when primary wave fails to clear gastric contents
Induced by distention of esophagus
Involves swallowing center and ENS
Occurs after vagotomy
What nerve acts through the Myenteric nervous system?
This controls what part of the esophagus?
Vagus
Mid and lower regions
When does gastroesophageal reflux occur?
Intra-abdominal pressure is increased (due to pregnancy, obesity)
What is released to mediate opening of the LES for receptive relaxation?
VIP and possibly NO
What is GERD?
Symptoms?
Result?
Abnormal relaxation of the LES
Heartburn, chest pain, dysphagia, lump in throat
Barret’s, stricture, asthma, sinusitis
What is achalasia?
Cause?
Symptoms?
Impaired peristalsis or lack of LES relaxation during swallowing or elevation of LES resting pressure
Damage to nerves in esophagus or abnormal immune system response
Weight loss, regurgitation, dysphagia, vomiting, chest pain
What layers of muscles does the stomach have?
Circular
Longitudinal
Oblique
What happens in the orad region of the stomach during receptive relaxation?
What kind of reflex is this?
DEC pressure, INC volume
Vagovagal reflex
What effect does CCK have on the stomach?
DEC contractions
INC gastric secretions
What does phase lag do as the peristaltic wave approaches teh antrum of the stomach?
DECREASES
What happens in the caudad region of the stomach to further mix and reduce particle size of stomach contents?
Retropulsion
What factors INC AP and force of contractions in the stomach?
PS
Gastrin
Motilin
What factors DECREASE AP and force of contractions?
Sympathetics
Secretin
GIP
How does the rate of gastric emptying INCREASE?
DEC distensibility of the orad, DEC tone of the pylori so
INC peristaltic contractions of caudad
INC diameter and inhibition of segmenting contractions of prox duodenum
What factors inhibit gastric emptying?
DEC peristaltic contractions
INC tone of pyloric sphincter
What receptors inhibit gastric emptying via what hormone?
Fat and proteins via CCK (INC gastric distensibility)
What does hypertonicity in the duodenum lead to?
Inhibition of gastric emptying
What is the most common problem associated with disorders of gastric motility?
Slow gastric emptying
What is gastroparesis?
Cause?
Symptoms?
Slow emptying of stomach/paralysis of stomach
Damage to the vagus nerve or high blood glucose
Nausea, vomiting, abdominal bloating, weight loss
How are large particles of undigested residue in the stomach emptied?
How is this mediated and how often?
MMC
Via Motilin in 90 minute intervals
Absence of MMCs in the stomach is assoc. with what?
Gastroparesis
What does segmentation contractions do?
Mix the chyme and expose it to pancreatic enzymes
What do peristaltic contractions do?
Propel the chyme towards large intestine
What contracts behind the bolus?
In front of?
Circular
Longitudinal
Describe initiation of contractions in the small intestine
Slow waves DO NOT initiate contraction
APs necessary
Slow wave freq. sets the max freq. of contractions
What has a higher higher slow wave frequency:
Duodenum or ileum?
What is the general trend?
Duodenum (12 cycles/min)
DECREASE in freq. toward ileocecal junction
What releases serotonin?
Where does it bind?
What does it initiate?
ECCs
Receptors in IPAN (intrinsic primary afferent neuron)
Peristaltic reflex (stimulates contractions)
What hormones stimulate contractions of the intestine?
Inhibit?
PGs, Gastrin, CCK, Motilin, insulin
Epi, secretin, glucagon
What coordinates the vomiting reflex?
Medulla
Describe the order of events of reverse peristalsis in vomiting
Reverse peristalsis of s.i. Relaxation of stomach and pylorus Force inspiration to INC abdominal pressure Movement of larynx Relaxation of LES Closure of glottis Forceful expiration of gastric contents
What stimulates the chemical trigger zone in the vomiting reflex?
Morphines, opioids
What relaxes the sphincter and excites peristalsis at the ileocecal junction?
Pressure and chemical irritation
What inhibits peristalsis of ileum and excites sphincter at the ileocecal junction?
Pressure or chemical irritation in cecum
What prevents passage of contents from the colon to the ileum?
Distention of the colon –> contraction of sphincter
Main fx of l.i.?
Absorb water and Vits
Convert digested food into feces
What portions of the Sympathetic N.S. Innervates the large intestine?
T10-L2
What is the sympathetic innervation of the distal rectum and anal canal?
Hypogastric plexus
What is the sympathetic innervation of the proximal large intestine?
SM ganglion
What is the sympathetic innervation of the distal large intestine?
IM ganglion
What is the sympathetic innervation of the external anal sphincter?
Somatic pudendal nerves
What are the major excitatory mediators of the large intestine?
Inhibitory?
ACh and Substance P
NO and VIP
Where do segmentation contractions occur?
Fx?
Cecum and ascending colon
Mix contents
What do mass movements stimulate?
How often?
Defecation reflex, propels feces into rectum
1-3 times/day
What does poor motility cause in large intestine?
Excess motility?
Greater absorption therefore hard stool –> constipation
Less absorption –> diarrhea
Where do rectal distention senses and voluntary control of the external anal sphincter pathways travel to?
Spinal cord to cerebral cortex
What is the rectosphincteric reflex under control of?
What happens in paraplegic patients?
Neural control
Lack tonic contractions, defecation
What is diverticulitis?
What causes it?
Where is the most common location?
Small sacs of intestinal lining that bulge outward in a weak spot
Excess pressure in colon
Left side of colon
What is motility important for?
Preparation of ingested food for digestion and absorption
