Gastrointestinal Motility Flashcards
What does motility refer to?
contraction and relaxation of walls and sphincters of the GIT
- accomplishes grinding, mixing, and fragmenting food
The contractile tissue of the GIT is composed of?
smooth muscle and striated muscle in upper 1/3rd of esophagus, external anal sphincter
What allows for very smooth contraction?
unitary smooth muscle
What does unitary smooth muscle have?
cells electrically coupled via gap junctions
signals spread rapidly —> allows for smooth contraction
List the types of contractions of smooth muscle in the GIT.
phasic contractions
tonic contractions
What does circular muscle do?
shortens ring of smooth muscle
- shortens DIAMETER
What does longitudinal muscle?
shortens in a longitudinal direction
- shortens LENGTH of SEGMENT
What are phasic contractions? Where does this occur?
periodic contractions followed by relaxation
- esophagus, gastric antrum, SI
What are tonic contractions? Where does this occur?
maintain a constant level of contraction or tone without regular relaxation
- upper region of stomach, lower esophagus, ileocecal, internal anal sphincters
Define slow wave of GIT.
unique to GI smooth muscle
oscillating repolarization and depolarization of membrane potential of smooth muscle cells
T/F: Slow waves may or may not bring membrane potential to threshold i.e. not always an AP
TRUE
More AP =
stronger contractions
The ______ has the highest contractions at 12/min, and the _______ has the lowest constrictions at 3/min.
duodenum
stomach
What is the origin of slow waves?
interstitial cells of cajal (myenteric plexus)
interstitial cells
What has depolarizations that occur simultaneously?
interstitial cells of cajal
What is the pacemaker for GI smooth muscle?
interstitial cells
Depolarization phase and maintenance of the plateau involves ________ in slow wave mechanisms.
opening of Ca2+ channels
Repolarization phase involves ________ in slow wave mechanisms.
opening of K+ channels
T/F: The frequency of slow waves are influenced by neural and hormonal output.
FALSE
List the 3 functions of mastication.
mix food with saliva to lubricate
reduce size of food particles
mix ingested carbohydrates with salivary amylase
What is the involuntary component of chewing?
mechanoreceptors in mouth relay to brainstem
- initiated by food in mouth
What is the voluntary component of chewing?
can override reflex chewing at any time
What is initiated voluntarily in the mouth?
swallowing (deglutition)
Where is the control for reflex swallowing located?
swallowing center in medulla
- receptors near pharynx detect and send information via vagus and glossopharyngeal nerves
What are the 3 phases in swallowing?
oral phase
pharyngeal phase
esophageal phase
Define oral phase.
voluntary at first then involuntary
- tongue forces bolus towards pharynx, involuntary swallowing takes over
Define pharyngeal phase.
involuntary, propel bolus from mouth through pharynx to esophagus in 4 steps
Explain the 1st step of the pharyngeal phase.
soft palate pulled up to narrow passage —> can’t move to nasopharynx
Explain the 2nd step of the pharyngeal phase.
epiglottis moves to cover the opening to the larynx
larynx moves up against epiglottis
- cover opening to trachea
Explain the 3rd step of the pharyngeal phase.
upper esophageal sphincter relaxes
food passes from pharynx to esophagus
Explain the 4th step of the pharyngeal phase.
peristaltic wave to propel bolus to sphincter
Define esophageal phase.
controlled by swallowing reflex AND enteric nervous system
- propels bolus to stomach
What is the primary wave to push the bolus?
swallowing reflex closes upper esophageal sphincter
What are the two waves in the esophageal phase?
primary peristaltic wave
secondary peristaltic wave (if needed)
What is mediated by the ENS?
primary and secondary peristaltic waves in the esophageal phase
T/F: The upper esophageal sphincter is closed unless bolus needs to pass through the esophagus.
TRUE
The primary peristaltic contraction creates _______
high pressure area behind bolus
When the peristaltic wave and bolus reach the lower esophageal sphincter, it _______, and is mediated by _______.
opens
vagus n. and VIP (neuromodulator)
When bolus reaches the lower esophageal sphincter, there is __________ in the stomach, which causes pressure to _______.
receptive relaxation of upper region of stomach
pressure DECREASES
The secondary peristaltic wave (if needed) _______
clears esophagus of any remaining food
T/F: There is a pressure difference between upper and lower esophagus which is important.
TRUE
What are the 3 components of gastric motility?
relaxation of orad region in stomach
contractions
gastric emptying
What is hormonally regulated?
gastric emptying
The caudad region is _______ for __________.
thick-walled
stronger contractions
The stomach has ______ and _______ innervation.
external
internal
What are the 3 muscle layers of the stomach?
outer longitudinal
middle circular
inner oblique
Receptive relaxation of orad stomach is caused by the relaxation of lower esophageal sphincter, which will ______ pressure and ______ volume of stomach
decrease
increase
What is the vasovagal reflex involved in? What limbs of the nerve?
receptive relaxation of the stomach
afferent and efferent
Contractions begin in the ______
caudad region of stomach
Waves begin in the ______
middle of body of stomach
The waves become more ______ the closer you get to pylorus
rigorous
During mixing and digestion, there may be retropulsion, which is ________
bolus propelled back, further reduction of particle size
For slow waves, neural input and hormones can’t alter frequency, BUT they can alter ________
contraction strength
Gastrin and motilin _______ force of contraction via _______
increase
PSNS
Secretin and GIP _______ force of contraction via _______
decrease
SNS
Migrating myoelectric complexes are mediated by _____ during fasting, to clear any remaining food.
motilin
What are the goals of SI motility?
mix chyme with enzymes and secretions
expose nutrients to intestinal mucosa for absorption
propel chyme to LI
Slow waves are more frequent in the ______
duodenum
There is parasympathetic innervation in the small intestine via the _______, which will _______ contraction strength
vagus nerve
increase
There is sympathetic innervation in the small intestine via the _______, which will _______ contraction strength
celiac and superior mesenteric ganglia
decrease
What does the enteric nervous system coordinate in the small intestine?
segmentation
peristaltic contractions
What are segmentation contractions
part of intestine that contractis to split digests and allow it to re-mix
How does segmentation contractions mix chyme?
back and forth movement
NOT FORWARD
For peristaltic contractions there is a ______ behind the bolus and _______ in front of bolus.
contraction behind
relaxation in front
You need the _______ and ________ to work together during peristalsis.
circular muscle
longitudinal lmuscle
What senses the bolus?
enterochromaffin cells
What are enterochromaffin cells?
cells that sense the bolus
involved in peristaltic reflex for moving chyme
What happens during vomiting?
information from vestibular system, back of throat, GIT, and chemoreceptor trigger zone in 4th ventricle
vomiiting center in medulla —> vomiting reflex
What happens during vomiting reflex?
reverse peristalsis in si
relaxation of stomach and pylorus
increased abdominal pressure
movement of larynx up
relaxation of lower esophageal sphincter
closure of glottis
forceful expulsion
Define retching
upper esophageal sphincter remain closed, lower open, contents return to stomach
What sphincter opens to allows contents into cecum, then contracts to close?
ileocecal sphincter
The colon in pigs forms a spiral colon where?
ascending colon
What has no sigmoid colon?
dog, cat, horse
Where do segmentation contractions occur in the large intestine? They are associated with _____
cecum
proximal colon
haustra
Define haustra.
sac-like segments
What has no haustra? What does?
NO: dogs, rats, carnivores, ruminants
YES: guinea pigs, rabbits, pigs, humans, monkeys, horses
Define defecation
rectum fills and smooth muscle wall contracts
internal anal sphincter relaxes
external anal sphincter tonically contracted until defecation
Define gastrocolic reflex. There is the afferent limb in the _______ and efferent limb in _______
distention of stomach increases motility of colon
afferent: stomach
efferent: colon
