Intro to GI U6L01 Flashcards
a series of musclar sphincters regulate unidirectional flow between diff sections of the gi tract via ___ mechanism
inherent myogenic
___ and ___ are necessary to promote digestion, absorption, and detoicfication of ingested materials
substantial fluid shifts and ph changes
the primary nerve nets or plexuses in the enteric NS are
myenetric and submuscosal
The myenteric plexus (Auerbach’s) is between the ___ and ___ layers of the GI tract
longitudinal and circular muscle
myentric plexus extends from the___ to the ___
esophagus to the rectum.
stimu. of the myeneric plexus increases ___ (3)
- increases tonic contraction or ‘tone’ of the gut
- the intensity of rhythmic /phasic contractions
- and velocity of conduction of excitatory waves (thus enhancing peristalsis)
The submucosal plexus (Meissner’s) is between the c
circular muscle and submucosa in the small and large intestines
primary function of the submuosal plexus
primarily involved with: controlling
- local intestinal secretions
- absorption
- contraction of the submucosal muscle which affects local infolding of the GI mucosa.
The sphincters are essentially ___-way valves
one
spchinters maintain a ___ pressure
positive
Activation of____ neurons leads to transient relaxation of the sphincters (causing release of food)
inhibitory motor
___ maintains the highest resting pressure of all sphincters
upper esophageal sphincter (UES)
upper esophageal sphincter (UES) prevents
air from entering the esophagus
sphinters made of skeletal muscle
upper esophageal sphincter
external anal sphincter
what controls the upper esophageal sphincter?
the swallowing center in the medulla
lower esophageal sphincter (LES) separates the ___ and ___
esophagus and the stomach
esophageal sphincter amde of smooth muscle
lower esophageal
lower esophageal sphincter (LES) functions
- to coordiante the passage of food into the stomach
- prevent the refleux of gastric contents
An incompetent ___can lead to heartburn/acid indigestion
LES
the resting pressure of the pyloric sphincter contributes to regulation of
gastric emptying
the resting pressure of the pyloric sphincter contributes to prevention of
duodenal-gastric reflux
Reflux of bile acids and digestive enzymes can lead to (3)
gastritis, ulcer formation, and risk of perforation
ileocecal sphincter is a valve-like structure that separates the ___ and ___
ileum and cecum
function of the ileocecal sphincter
reventing back flux of colonic contents into the ileum
. While we ingest ~2 liters (L) of fluid in food and drink each day, the GI tract adds____ of secretions to facilitate digestion and absorption of the nutrients.
~8 L
what in the GI system adds the most fluid?
pancreatic juice
___ absorbs the most fluid
small intestine
relatively, how much fluid is excreted in feces?
very little compared to what is absorbed, only 100-200 ml
____ in the oxyntic glands of the stomach acidify the contents of the stomach to promote digestion, and breakdown of ingested bacteria and antigens.
Parietal cells (oxyntic)
with acidic chyme in the stomach, the hydrogen ion concentration is ___ times that of the arterial blood.
~3 million
Secretion of HCO - into the lumen of the duodenum is by the ___
exocrine pancreas
___ by the exocrine pancreas neutralizes the acidic chyme being delivered from the stomach to duodenum.
Secreted HCO -
The two primary smooth muscle layers controlling motility are the___ and ___ muscles in the gut
e circular and longitudinal
enteric nervous sytem is called the minibrain
because of its plexuses
the ens is able to function indepdently responding to input from the local environment even in the abscense of
extrinisc innervation
musculomotor and secretomotors can alter
smooth m. activity
secretion and absorption of fluid/exlectrolytes
submucosal blood vessels
ENS activity is modulated by input from
the symps and parasymp
processing of sensory signals is a primary function of the ____ ENS neural network
intrinsic
sensory neurons monitor changes in luminal activity in the ENS
they activate ___. what does this do?
interneurons, which relay signals to activate efferent secretomotor neurons
Mechanoreceptors sense stretch of the smooth muscle, and the generated signal is transduced through the _____ plexus, stimulating contractions.
myenteric
Chemoreceptors sense the chemical composition of the chyme and regulate (2)
motility and secretion of buffers to control luminal pH during the influx of acidic chyme into the duodenum.
____receptors control the amount of chyme entering the small intestine
osmoreceptors
___ fibers (vagus and pelvic nerves) terminate on postganglionic cholinergic or peptidergic neurons located in the plexuses.
Parasympathetic preganglionic
____ activation leads to increased motility in the wall of the gut, relaxation of sphincters, and enhanced secretions
PNS
___ reflexes are prominent in coordinating GI function.
Vagovagal
The vagus innervates the proximal 2⁄3 of the ENS from the pharynx to the ___
beginning of the distal colon
The ___ nerves innervate the distal 1/3 of the colon
pelvic
the SNS innervates the enteric NS via postganglionic fibers from the (4)
- celiac plexus
- hypogastric
- and the superior & inferior mesenteric ganglia
SNS activation inhibits digestion and absorption by (4)
- relaxing the gut wall
- reducing secretions
- contracting sphincterss
- diverting blood flow from the GI tract by contracting the vasculature
what is the 5 layer heirachy that determines the moment to moment motor behavior of the digestive tract
___ are pacemakers in the gi tract that produce continual slow intrinsic exciation
intersitial cells of cajal
contraction of gi muscle wall occurs only when ___ are generated at the pearks of
the slow waves produced by interstial cells of cajal
2 types of waves produced by the ICC pacemakers
- slow waves – undulating changes in resting membrane potential
- spike pontetials – produced whent he threshold is reached during the paltea phase of the slow wave
how does PNS increase the contractility of the gi system?
by increasing the spike potentials of the pacemaker cells (not the frequency)
in GI, action potentials are produced largely by ___ entry through ____
Ca2+ entry through L-type VSCCs
The ENS controls the ___ and ___ of spread of electrical activity in the muscle using both excitatory (ACh, substance P) and inhibitory (VIP) motor neurons.
distance and direction
in the stomach there are ____ contractions in addition to the contractions generated to move food along
tonic contractions always occuring
____ connect the ICCs to the circular muscle.
Gap junctions
Slow wave motor patterns are influenced by (3)
hormones, paracrine factors, the ANS
Slow wave frequency is highest in the___
small intestine
Slow wave frequency is lowest in the
stomach
The maximal contractile frequency in the muscle does not exceed the
frequency of slow waves
Neural and hormonal input modulate the production of action potentials and thus the
strength of muscle contractions.
Failure of __can lead to disordered motility including spasm and abdominal cramping.
ENS control
small inestinal motility mixes and moves chyme by ___
segmental and peristaltic contractions
Segmental/mixing/non-propulsive Contractions are local events and typically occur in different segments at a frequency of ~___ per minute.
2-3
The maximal frequency of segmental contractions in the small intestine is no more than 12 per minute, and is determined by the___
frequency of electrical slow waves
Excitation from the___ plexus is important for Segmental/mixing/non-propulsive contractions
myenteric nerve
effect of atropine (muscarinic cholinergic anatagonist) on Segmental/mixing/non-propulsive contractions
weak contractions, showed the importance of the myenetric n. plexus
Peristaltic contractions - move material from __ to )))
mouth to colon
___ hrs are needed to move chyme from the pylorus to the ileocecal valve.
~3-5
Peristalsis is intensified after a meal by stretch of the duodenal wall upon entry of
chyme.
____ reflex enhances peristaltic motility and secretions.
gastroenteric
gastroileal reflex triggers opening of the ___ valve to permit passage of chyme from small to large intestine
ileocecal
distension of the ileum leads to ___ of the sphincter
relaxation
distension of the ascending colon leads to ___.
contraction
___ reflex decreases gastric motility and secretions
enterogastric
what does the enterogastric reflex stimulate?
contraction of the pyloric sphincter
intestinatal motlity after ingestion of a meal is characterzed by mixing to
optimize contact between ingested food and digestive secretions
intestinatal motlity after ingestion of a meal is characterzed by circulation of intestinal contents to faciliate
contact with the mucosa
intestinatal motlity after ingestion of a meal is characterzed by net propulsion of contents in a
aboral direction
____ forms pockets of chyme and serves to mix and propel the chym
Segmentation
rritation of the intestinal mucosa by infectious agents, for example, causes a
peristaltic rush/diarrhea that serves to clear the intestine of the irritant.
myentric reflex or law of the gut is also called
peristalsis
proximal to the bolus is something that causes ____ of the longitudinal muscle
excitation
distal to the bolus (the receiving end) is something that causes ____ of the circular muscle
relaxation
peristalsis occurs with the simultaneous shortenin and relaxation of the __ and __ muscles to move the bolus
the circular and longitudinal muscles
circular muscle or longitudinal muscles are thicker?
circular
circular muscle is innervated by ___ motor neurons
excitatory and inhibitory
longitudinal muscle is innervated by ___ motor neurons
excitatory
Physiological ileus is the
absence of motility in the small & large intestine
Is Physiological ileus normal or abnormal?
normal state.
with Physiological ileus, A subset of inhibitory neurons are active and suppress the response of the
circular muscle to the electrical slow waves.
Pathological ileus (paralytic ileus) is a state when the normal periods of quiescence are much ___.
longer
with Pathological ileus the inhiitory neurons are
abnormally active
altered motility and delayed transit is common after (3)
abdominal surgery (postoperative ileus), anticholinergic or opiate drug treatment.
Fasting is an interdigestive state that is characterized by
long periods of quiescence in conjunction with short rhythmic waves of strong propulsive contractions that pass down the distal stomach and small intestine.
short rhythmic waves of strong propulsive contractions during the resting phase are called
Migrating Motor Complex
3 phases of migrating motor complex
quiescence (I), little activity (II), and strong activity (III)
function of the migrting motor complex
‘sweep’ the stomach and small intestine of residue including undigested food/fiber, bacteria
during ___ the pyloric sphincter is inhibited and particles larger than 2 mm can pass into the duodenum.
migrating motor complex
migrating motor complex is observed ___
3 hours after the last meal
Migrating Motor Complex occurs in intervals of
90 minutes
where does the igrating motor complex start
Begins in the distal 1/3 of the stomach
Motilin is synthesized in the
duodenal Mo cells
motlin is released into the circulation and stimulates the
contractions (5-10 min) seen during the active phase
Motilin acts through the ___ to stimulate contractions.
ENS and ANS
in the absence of the MMC, indigestible material called ___ accumulate
“bezoars”
significance of “bezoars”
can obstruct the lumen of the stomach in particular.
effect of vagotomy on MMC?
reduces constracile acitivty
is MMC an intrisnic or extrinsic property of the gi tract
intrinsic
3 phases of swallowing
- voluntary stage
involuntary events
- pharyngeal phase
- esophageal phase
what does the volutnary stage of swallowing involve? (2)
- shaping of food into a bolus
- Raising of the tongue against the hard palate to create a pressure gradient that pushes the bolus
into the pharynx.
___ activates sensory neurons that project via the vagus and glossopharyngeal
nerves to the swallowing center in the medulla.
Food in the pharynx
Efferent impulses are sent back to the pharynx, esophagus, esophageal sphincters and stomach
causing: (3)
- the soft palate to pull upward (preventing food reflux into the nasopharynx)
- movement of epiglottis and pharynx to prevent food from entering trachea
- relaxation of the UES
what is the pharyngeal phase of swallowing
- soft palate pulling upward
- movement of the epiglottis and pharynx
The ___ also initiates a primary peristaltic wave that propels food through the open UES
swallowing reflex
with the opening of the LES and peristalsis of the esophagus the stomach
undergoes receptive relaxation
what happens If the primary wave fails to move all food into the stomach?
a secondary peristaltic wave results from distension of the esophagus
in the pahryngeal phase tactile areas in the pharnx transmit impusles tot he swallowing center in the ___
medulla
nerves activated during th epharyngeal phase include
5, 9, 10, 12
during the pharyngeal phase, the swallowing center of the medulla inhibits
the respiratory center
pharynx and upper 1/3 of the esophagus are ___ muscle,
striated
pharynx and upper 1/3 of the esophagus are controlled by skeletal nerve impulses from ___
CN 9 and 10
disorders of swallowing can occur with damage to nerves
5, 9, 10
diseases that damage the swallowing center include ___ and ___
poliomyelitis and encephalitis
___ and ___ are two diseases that can cause paralysis of the swallowing muscle
muscular dystrophy and myasthenia gravis
what is the signfiicance of the swallowing mechanism duirng sedation?
deep anesthesia inhibits the swalowing mechanism
its pts vomit on the operating table it will suck into the trachea instead of swallowing it
nuclei initiated during deglutition
nucleus ambiguus cn 9 and 10
dorsal mtoor nucleus of vagus
and tohers
pressure in UES after swallowing
pressure in LES after swallowing
pressure in stomach after swallowing
what is receptive relaxation?
transient relaxation of the proximal stomach with each bolus of food
Receptive relaxation in the lower esophageal sphincter and fundus is primarily regulated by a ___ reflex after swallowing
vagovagal
The transmitter released by the postganglionic vagal fibers during receptive relaxation?
vasoactive intestinal polypeptide (VIP).
The secondary wave begins at the point of ____ and travels downward.
distension
In the stomach, receptive relaxation results in an increase in intragastric ____
volume (not presure)
As food accumulates in the stomach there is a gradual _____ of the entire stomach, called accommodation,
relaxation
accodomation allows storage of food without an
increase in intragastric pressure
the ___ reflex mediats accommodation
vagovagal
gastric empyting is slow after
ingestion of a high fat meal
gastric empyting is _____ after ingestion of liquid salide
rapid
food entering the stomach does not cause a proportionate increase in intragastric pressure until a ___
threshold is reached (you really pig out)
if you cut the vagus, compared to normal the intraluminal pressure
increases much earlier with filling of food
Modification of gastric contents is associated with multiple feedbakc mechanism, most which arise from the
duodenum
modificaiton of gastric contents by the duodneum almost alays resuts in a
delay in gastric emptying
chemoreceptors and mechanoreceptors in the small intestine-sense (3)
- low pH (high acidity)
- a high content of calories, lipid, or some amino acids (i.e., tryptophan)
- or changes in osmolarity.
effect of cck on gastric contents?
CCK is a major player in decreasing the rate of gastric empyting
Delayed gastric emptying represents: the coordinated function of
- fundic relaxation
- inhibition of antral motor activity
- stimulation of isolated, phasic contractions of the pyloric sphincter
- altered intestinal motor activity.
when LES is incompetant, what two issues can you have?
achalasia and GERD
achlasia is due to
the failure of LES to relax during swallowing
The resting tone of the lower esophageal sphincter (LES) is usually ____
high, preventing reflux of stomach contents
As the bolus of food reaches the LES, local____ is released, and the sphincter tone relaxes
vasoactive intestinal peptide (VIP, and probably NO as well)
gastroesophageal reflux disease (GERD) cause?
failure of the ability to maintain LES tone
damage to the myenteric plexus in the lower 2/3 of the esophagus (smooth muscle) can cause the lower esophagus to be
spastically contracted (due to a lack of inhibitory motor neuron activity)
and unable to transmit the signal for receptive relaxation to the LES
functionally the stomach is divided into a
- proximal gastric reservoir – fundus and 1/3 of the body
- distal antral pump – caudal 2/3 of the body, antrum, pyloris
Muscles in the___ portions of the stomach are adapted for maintaining continuous contractile tone.
gastric reservoir
in the stomach, the ___ is where you get the phasic contractions
antrum
function of the gastric reservoir? (2)
- to accommodate arrival of a meal without a significant increase in intragastric pressure
- to maintain constant compressive forces on the contents of the reservoir which push the contents into the antral pump region
failure of the gastric reservoir leads to
bloating, epigastric pain, and nausea/dyspsiea
the ___ propels chyme towards the gastroduodenal junction
antral pump
Action potentials in the antral pump are ___.
myogenic
what nt release increases contractions of the antral pump
acetlyhcoline from the PNS
what nt release decreases contractions of the antral pump
norepinephrine contractions from the SNS
the ___ churns the trapped bolus
antrum
when the pylorus is closed, what happens after grinding?
processes of propulsion, grinding, and retropulsion repeat multiple times until
the gastric contents are emptied.
Particles larger than____ are initially retained in the stomach but are eventually emptied into the duodenum by MMCs during the interdigestive period
2 mm
