•GI motility Flashcards
the migrating myoelectric complex is active from the ____ through the _____
midstomach, terminal ileum
the migrating myoelectric complex begins ____ hours after you finish eating
3-4
___ produces a series of serial contractions that sweep material into the colon. It lasts about ___ per cycle and is caused by secretion of the hormone ____
Phase III of MMC
10 minutes
motilin
and entire MMC cycle lasts ____
75-120 minutes
motilin is secreted by ____
M cells of the duodenum (small intestine)
swallowing begins as a _____ but becomes _____ as the ____ and _____ nervous systems take over
voluntary action, involuntary, enteric, autonomic
primary vs. secondary esophageal peristalsis
primary: vagal, signals go back to the brain’s swallowing center and medulla secondary: more local, enteric nerves help out, if something gets stuck
achalasia
a smooth muscle disorder in which the lower area of the esophagus and LES doesn’t have enteric nerves
- LES cannot relax, food can’t get into stomach
- typically will have a dilated esophagus, and many develop anorexia.
gastric accommodation is able to occur because of the ____
vagus nerve anticipation
the narrowed area at the bottom of the stomach:
antrum
organize the following by speed of gastric emptying: oleate meal (fat), saline meal, acid meal (protein)
saline, acid, oleate
hormones that regulate the rate of gastric emptying come from the ____
duodenum
the basic electrical rhythm of the GI tract is generated by:
ICC- interstitial cells of cajal
the basic electrical rhythm is associated with ____
metabolism
the ICC rate of stomach is:
3/min
the ICC rate of the small intestine is:
10-12/min
the ICC rate of the colon is:
variable
the action potentials at the top of resting membrane potential slow waves causes:
calcium to be released which binds to calmodulin and activates myosin to cause a contraction
what are things that can depolarize the slow waves?
stretch (presence of chyme), ACh/parasympathetics (vagus), gastrin, serotonin, tachykinin
what are things that can hyperpolarize the slow waves?
NE, sympathetics, VIP, NO
_____ helps mixing in addition to propulsion
segmentation
describe the release of bile after ingestion of food:
the vagus nerve stimulates bile production in anticipation. When chyme reaches the duodenum, it secretes CCK. CCK stimulates rhythmic contractions of the gallbladder which releases bile into the duodenum. The vagus also relaxes the sphincter of Oddi (where the common bile duct enters into the duodenum)
the majority of the time, it is ____ that is the dominant force of propulsion in the colon
segmental propulsion
segmental propulsion is achieved by bands of longitudinal muscle called ______
taneia coli
sacs formed by taneia coli for reabsorption:
haustrae
what are the two types of propulsions in the colon?
mass movements and segmental propulsion
gastrocolic reflex
food in the stomach causes colonic mass movement, due to vagus and gastrin
rectosphincteric reflex
rectal stretch stimulates a defecation response
Hirshsprung’s disease
aka Megacolon: ENS / enternic nerves are absent from lower colon, rectum and internal anal sphincter. The normal defecation reflex does not occur: IAS remains constricted, and the colon becomes dilated.
- congenital disorder, usually diagnosed when child is several months old.
- Treatment: excision of lower colon and rectum, and reanastamosis with external sphincter. child is trained to defecate in a normal manner as a toddler.
Motilin and Gastrin are ______ hormones, and thus, are secreted into ____
Motilin and Gastrin are endocrine hormones, secreted into the blood
Where is Gastrin produced and when is it released?
- produced from endocrine G cells located in the gastric glands of the antrum (stomach) and duodenum
- is secreted into the blood in response to stretch and the composition of the chyme (carbs, proteins, fats).
2 functions of gastrin
- Major action: enhances HCl secretion from the gastric parietal cells
- Early in feeding, when chyme is in stomach and duodenum, gastrin stimulates motility in ileum and colon (in conjunction with PNS) to make room in the colon and push out feces.
Factors that depolarize slow waves include ___
- stretch
- substance P (tachykinin)
- ACh (PNS)
- serotonin
Factors that hyperpolarizeslow waves include ____
- NE (SNS)
- nitric oxide (NO)
- vasoactive intestinal peptide (VIP)
What generated the slow waves in the GIT?
Interstitial cells of Cajal (ICC) between the longitudinal and circular smooth muscle layers.
What is the SIP syncytium?
- coupling of the smooth muscle in the GIT to the ICC and a PDGFR-α+ cell, forms a SIP syncytium.
smooth muscle + Interstitial Cells of Cajal + PDGFR-α+ cell
The undulations in the slow waves reflect changes in the RMP caused by ……..
coupling of the smooth muscles to the ICC and a PDGFR-α+ cell, forming a SIP syncytium
The SIP syncytium is regulated by ___
primarily pottasium (K+) ion channels and receptor-mediated processes
What is the BER?
- Slow waves are termed Basic Electrical Rhythm or BER
- because they are ALWAYS present, but their frequency (waves/min) is set by pacemaker cells, which change down the tract.
What sets the BER?
Different pacemaker cells throughout the GIT.
What is the BER/frequency of slow waves in the stomach and the small intestine?
slower in stomach (3 waves/min)
faster in small intestine (10-12 waves/min)
when the resting potential is <40 mV, _____
- there are essentially no contractions.
- spike potentials (AP) are generated on the peaks of the slow waves when RMP is depolarized above -40 mV.
Depolarization above -40 mV by ____ will stimulate APs, and the greater the depolarization, _____
- by stretch or parasymp stimulation
- the more APs, and the greater the contractions
The number of action potentials generated on a slow wave are directly related to ____
the force of contractions.
_____ will stop APs and contraction.
hyperpolarization (ie by sympathetic tone) will stop APs and contraction of GIT smooth muscle
Kinds of propulsion that takes palce in the Small intestine
Peristalsis and Segmentation
Describe difference between the 2 kinds of propulsion seen in the small intestine.
Peristalsis: contraction of circular smooth muscle “behind” the bolus, relaxation of the muscle distal/in front of to the bolus, moves bolus along the tract. Accomplished through stimulatory and inhibitory interneurons, may have more extrinstic (PNS) input.
Segmentation: mixes and propels, circular muscle contracts on either side of the bolus. Due more to local factors (eg stretch).
What are the two types of propulsion seen in the colon (large intestine)?
Segmental propulsion
Mass movements
Segmental propulsion
- occurs in the colon/large intestine
- caused by the contraction of longitudinal bands of tanea coli, form pockets of chyme called haustra. - These pockets remain for long periods, allow additional reabsorption of sodium and water (colonic salvage), producing feces.
what are haustra? tani coli?
- tani coli - longitudinal muscles on the colon
- haustra - when the tanai coli contract they cause chyme in the colon to form pockets called haustra
Mass movements
- occur in the colon, are more peristaltic in nature, occur 3-4 times/day coincident with feeding (gastrocolic reflex).
When a mass movement is stimulated, _____ relax, and peristaltic contractions in _______ move chyme and feces distally, towards rectum.
the haustra relax!
contractions in ascending and transverse colon
Gastrocolic reflex:
chyme in the stomach (gastro), stimulates colonic mass movements (colic) –> Moves chyme and feces out of lower GIT to prepare for more food
Describe nerves/hormones involved in Gastrocolic reflex.
- involves stimulation of Parasympathetic NS:
- vagus nerves– through the transverse colon
- pelvic nerve – from transverse to descending colon
- gastrin– (hormone from antrum and duodenum, both of which are stimulated very early in feeding)
- vagus and gastrin both stimulate depolarization of slow waves lower in the GI tract (ileum, ascending and T colon), initiating peristaltic-type movements.
Ileogastric reflex:
- chyme in the ileum (ileo-) slows gastric emptying into duodenum (gastric). Buys more time to clear the lower GIT
- When motility in ilium increases via gastrocolic reflex, this signals pylorus to increase sphincter tone, and reduce the amount of chyme leaving stomach.
Rectosphincteric reflex
Defecation reflex: Feces in the rectum relaxes the internal anal sphincter and we feel the urge to defecate.
- dependent on enteric nerves, which respond to mechanoreceptors in the rectum (stretch!) by relaxing IAS and send a reflex to the brain stimulating the urge to defecate. We then constrict the external anal sphincter until ready to go!
