PHYS: GI Motility Flashcards
What is aclasia?
failure of esophagus to relax
What happens when a food bolus reaches the back of the mouth?
reflexive swallowing contraction
What starts the wave of food down the esophagus?
primary peristalsis
What is the relative pressure at the upper esophageal sphincter?
pressure in esophagus > atmospheric pressure
What is the role of the UES?
when a bolus is swallowed, it opens to allow food to pass from the pharynx to exophagus
What stimulates the closure of the UES after a swallow?
pressure in the esophagus increases to close UES and the peristaltic wave begins
What is the pressure between the UES and diaphragm?
pressure < atmosphetic pressure (intrathoracic pressure is negative, making the esophageal tube flaccid)
What keeps the food moving between the UES and diaphragm?
peristaltic wave
What is the pressure after the diaphragm?
pressure > atmospheric pressure
What happens when the food bolus reaches the diaphragm?
LES relaxes as vagus releases VIP (increases NO for SM relaxation)
What occurs even BEFORE the relaxation of the LES to prepare for movement of the bolus into the stomach?
relaxation of the orad stomach
What structures are responsible for swallowing?
pharynx and the upper 1/3 of the esophagus (striated skeletal muscle–> voluntary)
What innervates the pharynx and the upper 1/3 of the esophagus?
directly innervated by vagus nerve (opposed to SM which must have the vagal stimulus relayed through myenteric ganglia)
List the 3 main phases of swallowing.
1) oral phase
2) pharyngeal phase
3) esophageal phase
Where does the oral phase of swallowing originate?
swallowing center of the medulla
What stimulates the oral phase of swallowing?
sensory information (ex. food in the mouth) is detected by somatosensory receptors located near the pharynx→ vagus and glossopharyngeal nerves carry information to medullary swallowing center→ motor output to striated muscle of pharynx and upper esophagus.
True or false: the swallow reflex is voluntary?
FALSE (involuntary)
What occurs during the pharyngeal phase of swallowing?
propel food bolus from moth to esophagus (soft palate up, epiglottis covers larynx and prevents food food from entering trachea), UES relaxes, primary peristalsis begins at pharynx.
What controls the esophageal phase of swallowing?
controlled partly by swallowing reflex and partly by enteric nervous system
What happnes during the esophageal phase of swallowing?
food is propelled into the stomach
What is a secondary peristaltic wave?
wave that is stimulated if there is food left behind and “cleans up” after the primary wave
What is receptive relaxation?
the orad stomach relaxes before LES relaxation then relaxes more and more as more food comes in
What type of reflex is receptive relaxation?
vago-vagal reflex
Describe the vago-vagal reflex in receptive relaxation.
both afferent (mechanoreceptors sense distention of stomach and relays it to CNS) and efferent (information to smooth muscle wall of orad stomach to relax after stimulated by VIP) limbs of the reflex are located in the vagus nerve.
What is one of the underlying problems that causes GERD?
failure of secondary peristalsis to eliminate acid in the esophagus (and this remaining acid causes erosion)
What other things can predispose to GERD?
- Failure of LES closure
- Pregnancy
- Hiatal hernia (part of stomach goes into thorax and negative pressure sucks up gastric acid)
What are the “pacemaker cells of the stomach”?
Interstitial cells of Cajal
Where are the interstitial cells of Cajal located?
myenteric plexus
How do the interstitial cells of Cajal work?
These depolarize due to cyclic opening of Ca2+ channels (like the SA node), spread the depolarization through low-resistance gap junctions, and continuously produce slow waves
What do slow waves of interstitial cells of Cajal lead to?
1) tonic contractions (subthreshold slow waves that do not lead to APs)
2) phasic contractions (if membrane is depolarized to threshold and AP occurs).
What determines the strength of the phasic contraction?
The greater the number of APs that occur on top of the slow waves, the stronger the phasic contraction!
True or false: the frequency of slow waves is always constant.
TRUE
True or false: the amplitude of slow waves is always constant.
FALSE: amplitude of slow waves is greater in the lower stomach
What do neuronal and hormonal activity alter in regards to slow waves?
nothing! they alter the frequency of APs (and thus the force of phasic contractions)
What leads to increased frequency of APs and strength of gastric contractions?
- Outside digestive processes (gastrin and motilin)
- Strong parasympathetic activity (lots of food)
What leads to decreased frequency of APs and strength of gastric contractions?
- Outside digestive processes (secretin and GIP)
- Sympathetic stimulation
What portions of the stomach are included in the “orad area”?
fundus and proximal body of the stomach
Waht types of glands are located in the “orad stomach”?
oxytinic glands
What is the role of the “orad area”?
storage
What portions of hte stomach are included in the “caudad area”?
distal portion of the body and the antrum
Which is thicker, the orad or caudad area of the stomach? Why?
caudad area (oblique SM in antral layer of stomach gives it an incrased thickenss compared to body/fundus)
What is the role of the”cauded area”?
Mixing
Emptying
Where do waves of contraction of the stomach begin?
middle of the body of the stomach and move distally along the caudad stomach (increasing in strength as they approach the pylorus)
Why is the chyme not immediately pushed into the duodenum with contracton of the stomach?
the contraction closes the pylorus
What is retropuslion?
most of the gastric contents are propelled back into the stomach for further mixing/reduction of particle size after being pushed into the duodenum
Why does the rate of gastric emptying need to remain pretty constant?
to allow for adequate gastric H+ neutralization and digestion/absorption of nutrients
What are symptoms of slow emptying?
fullness
loss of appetite
nausea
What are symptoms of increased gastric emptying?
diarrhea
duodenal ulcer
Do gastric ulcers SLOW or SPEED gastric Emptying?
SLOW
Do hypertonic solutions SLOW or SPEED gastric Emptying?
SLOW
Do hypotonic solutions SLOW or SPEED gastric Emptying?
SLOW
Do isotonic solutions (that cannot be broken down) SLOW or SPEED gastric emptying?
SPEED
Do solid foods SLOW or SPEED gastric Emptying?
SLOW
Do fats SLOW or SPEED gastric Emptying? Why?
SLOW (stimulate CKK when it reaches duodenum→ decrease pressure of orad stomach, slows gastric emptying, increase pressure in duodenum to push back on pylorus)
Do liquids SLOW or SPEED gastric Emptying?
SPEED
Does high acidity SLOW or SPEED gastric Emptying? Why?
SLOW (detected by duodenal H+ receptors→ enteric nervous system interneurons deliver message to gastric SM→ slow emptying time to permit time for neutralization by pancreatic HCO3-)
Does a vagotomy SLOW or SPEED gastric Emptying?
SLOW
How long does it typically take a meal to be emptied from the stomach?
2.5-3 hours
True or false: the small intestine has a greater slow wave frequency than the stomach.
TRUE (declines as you get closer to the ileum)
What is the relative slow wave frequency of the small intestine?
7-8 contractions per minute
What are the two types of small intestine contractions that can occur?
Segmental contractions
Peristaltic contractions
What is the role of segmental contractions?
mixing the chyme
How do segmental contractions work?
wave occurs in the middle of the bolus and sends it in two different directions and relaxation allows it to come back together (no net forward movement)
What is the role of peristaltic contractions?
propel the chyme toward the large intestine
How do peristaltic contractions work?
contraction occurs at a point behind bolus to push it forward (but not continuous down the entire length).
What stimulates a peristaltic contraction?
enterochromaffin cells of the intestinal mucosa sense the food bolus and release serotonin to stimulate a peristaltic reflex (contraction behind bolus and relaxation in front of bolus)
True or false: amplitudes are constant in the small intestine.
TRUE
What controls whether or not contractions occur?
“spiking”
Waht is a migrating motor complex?
contractions that occur every 90 minutes in fasting individuals to remove any residual chyme int he small intestine by propelling it down toward the colon
What controls migrating motor complexes?
nervous stimulation of motilin
What happens when the material in the small intestine reaches the cecum and proximal colon (distention of colon)?
iliocecal sphincter contracts to prevent reflux into the ileum
What relaxes the tonically contracted iliocecal sphincter?
distention of hte ileum
What type of reflex is the iliocecal reflex?
intramural reflex (contained within the walls of the terminal ileum and proximal colon)
What is the role of the large intestine?
store, absorb water, and evacuate material from the body
What is “mass movement”?
the haustra (pouches) disappear over a significant segment of the colon and a peristaltic contraction occurs
How often do colon contractions occur?
2-3 times during the day
What keeps the internal anal sphincter tonically contracted?
dorsal root segments
What is the retrosphincteric reflex?
when material reaches the rectum, the pressure increases and the internal anal sphincter relaxes—causing an urge to defecate (external sphincter automatically contracts (due to autonomic nervous system))
If you do not defecate immediately after getting the urge (from material in the rectum), what happens?
internal sphincter will contract and the urge to defecate goes away
What happens when defecation is convenient?
Voluntary relaxation of the external sphincter via the pudendal nerve and valsalva maneuver will cause defecation
