GI Tract Motility Flashcards
what two main functions does normal motility patterns help facilitate?
digestion/absorption
maintains aboral propagation
what are the main functions of the mouth and pharynx?
food prehension
mastication or chewing
swallowing/deglutition
describe the voluntary initial stage of swallowing/deglutition
movement of bolus to back of oral cavity
describe the involuntary pharyngeal stage of swallowing/deglutition
passage from oral cavity to esophagus
describe the involuntary esophageal stage of swallowing/deglutition
passage of food into stomach
list the flow of the food bolus during the swallowing process
back of oral cavity -> esophagus -> stomach
define transit time
travel time from one portion of gut to the next
if propulsive motility increases, transit time __ and vice versa
decreases
food bolus is transported via ___
peristalsis
what generates peristalsis in esophagus?
STRIATED muscle portion of esophagus is N by brainstem LMN from nucleus ambiguous
peristalsis occurs when a central pattern generator causes coordinated contraction from __ to ___
orad to aborad
a ___ arc facilitates esophageal peristalsis
reflex arc
describe the steps of peristalsis in the esophagus
- stretch receptors in esophagus wall are stim by distension
- sensory afferents transmit impulses to DMN
- DMN activates somatic and vagal efferent neurons
- cranial and caudal sphincters prevent food/air to enter esophagus
what is the dorsal motor nucleus (DMN)?
receives afferent sensory when esophagus is distended
activates somatic/vagal efferent
what does the lower esophagus sphincter (LES)?
barrier to prevent regurgitation of stomach content
the peristaltic wave propels the bolus down towards the LES, which is coordinated by…
swallowing center in medulla
the LES is ___ at rest
closed
once the bolus reaches the LES, it ___ to open, then ___
relaxes to open for bolus entry
then contracts to close once in stomach
what 3 mechanisms are involved in regulating LES tone
- ACh favors contraction
- NO favors inhibition
- tonic myogenic property favors contraction
describe the tonic myogenic property contraction process in regards to LES tone
sphincter wall stretch -> stretch receptor activated -> Ca channels open -> Ca influx to smooth muscle -> contract
the balance between ___ and ___ is required for normal LES activity
NO (inhibit) and Ach (excite)
describe the excitatory pathway for LES
neurons from DMN stim postgang cholinergic ENS neurons to release ACh and substance P
describe the inhibitory pathway for LES
DMN stim enteric ganglia postgang neurons which releases NO, VIP, ATP
what would happen to peristalsis or LES if either ACh or NO receptors where NOT activated?
myasthenia gravis (excitatory part absent)
how does dysmotility occur with Myasthenia gravis?
Ab’s block or destroy ACh receptors
inhibits contraction of esophagus, so NO food propelling
what is indicated by the radiograph?
megaesophagus
combo of disorders where esophagus loses motility since dilation
achalasia is a ___ disease
neurodegenerative
what is achalasia?
degeneration of inhibitory neurons of myenteric plexus
relaxation of sphincter becomes more restricted
what happens to the LES during achalasia?
relaxation of LES becomes more restricted
LES remains contracted, so ingesta cannot pass through
what is esophageal diverticula?
weakened esophageal wall or exposure to abnormal stress
how do the mediastinal lymph nodes cause diverticula?
granulomatous inflammation of lymph nodes
nodes pull on esophagus during peristalsis, causing conical outpouch
what generates motility of stomach, SI, and LI?
baseline is done via interstitial cells of Cajal
what are slow waves?
undulating electrical waves of partial depolarization
due to CAJAL CELLS
what occurs when the slow wave crest comes closer to zero?
AP, causing smooth muscle contraction
which molecules are released from ENS or paracrine cells to help elevate slow wave baseline?
EXCITATORY
ACh, substance P
which molecules lower slow wave baseline?
NO and VIP
contractions can occur no faster than the ___ of the slow waves
frequency
what factors modulate slow wave potential beyond threshold?
stretch/pH/nutrients
parasympathetics
GI hormones
hyperpolarizing of cells could ___ muscle activity
diminish/abolish
what inhibitory hormones/substances hyperpolarize ICC?
sympathetics
VIP and NO
why does new food trigger increased motility?
activates intrinsic endocrine and stretches wall
ICC reaches threshold
Ca releases from sarcoplasmic reticulum to cause smooth muscle excitation
what does the GI tract use to spread motility across tract?
gap junctions = transmit electrical activity
what’s the frequency of slow waves in stomach, SI, colon?
the ___ region of stomach acts as storage function, while the ___ portion is breaking down into smaller pieces
proximal
distal
what are the three components of stomach motility?
- adaptive relaxation of proximal stomach to accept food
- mix motions to reduce bolus size
- propulsion of chyme past pyloric valve at distal end into duodenum
what are the three basic motility patterns of the stomach?
adaptive relaxation
intensive slow waves
interdigestive motility complex
ID stomach components
what is adaptive relaxation of the stomach?
proximal part relaxes for food to enter
explain how the stomach relaxes for adaptive relaxation
ACh release -> ENS neurons and DMN activated -> ENS releases NO (relax fundus)
what is the intense slow waves of the stomach?
reflex response of distal region to food entering stomach
causes mixing
peristalsis waves from body to antrum to pylorus
why is the emptying mechanism of the stomach so tightly controlled?
since SI digestion/absorption takes time
LIMITING FACTOR IS SI
how is stomach motility inhibited?
response to distension, low pH, high fat in duodenum
how does CCK affect stomach emptying into duodenum?
secreted in response to fat in duodenum, inhibits antrum motility
how does secretin affect stomach empty into duodenum?
secretes due to low pH in SI and inhibits antrum motility
what is the enterogastric reflex?
rate of gastric emptying matches the SI rate of digestion and absorption
what is the interdigestive motility complex of the stomach?
relaxation of pylorus while strong waves of peristalsis move over the antrum
forces remaining items into duodenum
what hormone stimulates the interdigestive motility complex?
motilin
pylorus prevents __ movement
retrograde
what three main motility patterns are observed in SI?
segmentation
peristalsis
migrating motility complex (MMC)
what is segmentation of SI?
nonpropulsive mixing pattern
food bolus travels short distance in both directions, helps mixing
what is migrating motility complex (MMC) of the SI?
occurs during INTERDIGESTIVE PERIOD, when main part of food has passed
strong contractions which travel along entire SI
causes forceful SI emptying
what does the ileo-cecal sphincter do?
prevents retrograde movement into ileum
main functions of large intestine
nutrient, water absorb, fermentation, storage, release fecal matter
list the three important points of motility in the large intestine
colonic segmentation
colonic retropulsion/propulsion
mass movement
explain colonic segmentation
VERY SLOW (min)
mostly mixing, very little propulsion
aids in absorption of water and electrolytes
slow moves allow for significant bacteria growth
describe colonic retropulsion/propulsion
slow waves initiated by ICC in colon
ENS CAN SWITCH DIRECTION TO HAVE IT MOVE BACK TOWARDS MOUTH
intense mixing
explain LI mass movements
colon segments contract in sequence, drives feces rapidly through colon distally for defacation
what are the two sphincters of the anus?
internal of smooth
external of striated muscle
explain the retrosphincteric reflex
when feces enter rectum, internal sphincter relaxes and rectal wall contracts peristaltically to cause defecation
where in the body does sand accumulate in horses with sand colic?
colon, weighs down intestine and mechanically impairs motility
what occurs in patients with megacolon?
congenital absence of inhibitory neurons in submucosa and myenteric plexus
where is the vomiting center located?
reticular foramen of medulla (integrates signals)
where does vomiting center receive signals from?
- higher center
- vestibular apparatus
- vagal afferents from GI
- chemoreceptor trigger zone response to drugs
what is the chemoreceptor trigger zone?
area of reticular formation of the medulla under floor of 4th ventricle
senses chemical abnormalities (drugs, hypoxia)
