GI Motility Flashcards
Which of the regional motility patterns involves intestinal smooth and regular skeletal muscle?
Swallowing and defacation
opiods have (constipating/laxative) effect. How so?
Constipating, promote absorption of fluid and electrolytes
Parasympathetic regulation of the myenteric plexus involve (pre/post) ganglionic neurons while sympathetic involve (pre/post) gaglionic neurons.
Parasympathetic = pre ganglionic
sympathetic = post ganglionic
3 important inhibitory motor neurons of the ENS
VIP, ATP, and NO
List 6 important interneurons of the ENS
5HT GABA Ach Dopamine Enkephalin Somatostatin
Serotonin
- Net effect on motility:
- Net effect on mucosal secretion/absorption:
- pro-kinetic
- stimulates fluid and electrolyte secretion
Dopamine
- Net effect on motility:
- Net effect on mucosal secretion/absorption:
- anti-kinetic
- complicated
Enkephalin (opiate)
- Net effect on motility:
- Net effect on mucosal secretion/absorption:
- promotes symmetric segmentation
- stimulates fluid and electrolyte absorption
Acetylcholine
- Net effect on motility:
- Net effect on mucosal secretion/absorption:
- pro-kinetic
- stimulates fluid and electrolyte secretion
Vasoactive Intestinal Peptide (VIP)
- Net effect on motility:
- Net effect on mucosal secretion/absorption:
- as neurotransmitter: relaxes ISM
- In excess: secretory diarrhea
- stimulates fluid and electrolyte secretion
Which region(s) of the GI tract contains only skeletal striated muscle?
Mouth, pharynx, and upper esophageal sphincter (UES)
Which region(s) of the GI tract contains a mixed striated/smooth muscle?
Esophagus (1/3 striated, 1/3 striated/smooth, 1/3 smooth muscle) and anal sphincter
Which 6 regions only contain smooth muscle?
- stomach
- duodenum
- jejunum
- ileum
- colon
- rectum
The motility patterns of these two regions involve mostly segmentation, periodic local peristalsis, and mass movement
Colon and rectum
Once we start chewing and the food reaches a certain part of the pharynx, a ____ occurs which includes a swallow, then an _____ of contraction that goes down entire esophagus
- peristaltic wave
- orderly wave
What must happen way ahead of the arrival of the orderly wave? Why?
The lower esophageal sphincter relaxes (LES)
-ensures that bolus of food enters the stomach
In contrast to vascular smooth muscle, intestinal smooth muscle cannot respond to synaptic input unless it is also innervated by what?
Intestinal Cells of Cajal (ICC) (they are the pacemakers!)
What are the Intestinal Cells of Cajal? What is an important feature they contain?
- Cells that form a network over the ISM and are auto-excitatory
- pacemaker activity to generate rhythmic depolarization-repolarization pattern in ISM = slow wave rhythm = bioelectric rhythm
ISM only responds to synaptic input from enteric neurons when the ISM membrane potential is in the ____ phase of the slow wave pattern
Plateau phase
When the ISM is innervated only by the intestinal Cells of Cajal, what happens? What doesn’t happen?
It develops muscle tone but no motility patterns.
Motility patterns are programmed in the ___
enteric ganglia
Swallowing is a reflex initiated by food bolus by activating ___ in the _____
stretch receptors (GVA), pharynx
The GVA stretch receptors activated by bolus of food synapse in the ____, which then sends upper motor neuron output to the which two nuclei?
- Nucleus tractus solitarius
- nucleus ambiguus and vagal nucleus
What are the two things that happen to the proximal portion of stomach when food arrives?
- relaxes (receptive relaxation)
- minimal mixing of contents
When the distal portion of the stomach senses food, what does it initiates?
Propulsive waves (via local enteric reflexes) starting in upper 1/3 of stomach and ending at pylorus.
What happens to the pylorus just before the food is propelled toward the pyloric region? Why is this necessary?
The pylorus closes. –insures that oly chyme particles will leave the stomach during this gastric phase of digestion
What is the predominant motility pattern in the small intestine during the intestinal phase of digestion?
What is it during the inter-digestive period?
digestion: asymmetrical segmentation
interdigestive period: periodic MMCs
What are MMCs
Migrating motor complexes:
- waves of activity through the intestines in a regular cycle during a fasting state.
- trigger peristaltic waves, which facilitate transportation of indigestible substances through the small intestine, past the ileocecal sphincter, and into the colon
Serves a cleansing role–makes sure crap that got left behind during digestive period is expelled from stomach–discourages bacterial growth
MMC
The MMC is initiated what region?
Go through cascade that prompts the MMC
Pacemaker region–distal stomach
Prompted by vagus –> release motilin –> acts on enteric neurons in pacemaker region to start propulsive pattern
Dysfunction of what disrupts the MMC?
autonomic dysfunction
Predominant motility pattern of colon
symmetrical segmentation–simple mixing without net movement
3 types of control of defecation
- local reflex
- autonomic
- voluntary
Major changes in esophageal function with scleroderma
attacks smooth muscle so esophagus and sphincter is impacted
- slight delay in UES
- decreased middle esophagus and lower
- decreased LES
Major changes in esophageal function with Achalasia (failure of smooth muscle fibers to relax)
Pressure is too high so food is not passing through and getting stuck
- slight delay in UES
- slight decrease in upper esophagus
- decrease in middle and lower esophagus (not as dramatic as scleroderma)
- decrease LES
Major changes in esophageal function with Diffuse esophageal spasm
- wave like pattern of middle and lower esophagus
- increased duration of LES
Major changes in esophageal function with pharyngeal paralysis (like in muscular dystrophy or Parkinson’s–skeletal muscle is impacted, smooth muscle is ok)
- all affected except middle and lower esophagus
- LES is normal but has slight sigmoid curve)
What does effect does vagotomy (resection of vagal nerve) have on intraluminal pressure during gastric accommodation of food?
-stomach wont have as large of a compliance and pressure goes up tremendously with increase in volume
- need an intact vagus in order to have receptive relaxation of stomach!
- also need intact ENS but can’t do job alone
In looking at a graph comparing the change in diameter of the proximal and distal stomach during gastric phase of digestion, the proximal stomach stays relatively constant meanwhile the distal goes up and down in wave like matter. Why?
Proximal stomach does not have a lot of contraction meanwhile the distal undergoes contractile movements
CCK effect on gastric emptying–what do you see on graph
slows down rate so will see food remain in stomach longer as time progresses
What is the effect o fnausea on gastric emptying?
delays emptying
-and vice versa: delayed emptying can cause nausea
One complication of long-standing diabetes is loss of ANS function. How does this affect gastric transit and acid secretion during the gastric phase?
transit time: slower (longer)
HCl secretion: no change
Gastrocolic reflex is an example of autonomic regulation of ENS. Helpful in regulating digestion and absorption but not necessary. describe it
gastric distension –> GVA via vagus to NTS —(interneurons)–> preganglionic parasympathetic neurons in sacral spinal cord —pelvic splanchnic nerves—> myenteric neurons in distal colon –> increased motility and mass movement in distal colon
is motor activity in the colon all coordinated?
- Sometimes, activities are coordinated
- mass movement of transverse and descending occur at different times
- Anal sphincter and rectum seems to have life of its own
Internal anal sphincter is what time of muscle and innervated by what nerve?
- thickening of intestinal smooth muscle
- pelvic splanchnic nerve
External anal sphincter is what type of muscle and innervated by what nerve?
Skeletal muscle, peripheral nerves (pudental nerve)
The internal anal sphincter works similar to what esophageal sphincter?
LES
-when food reaches canal, relaxes
How does external anal sphincter work
Almost immediately , EAS quickly takes over and keeps anus closed. Good sot hat we dont have to take a shit every time the rectum undergoes a propulsive movement
*NEED INTACT INNERVATION THOUGH!
Internal anal sphincter is (voluntary/involuntary) while the external is (voluntary/involuntary)
internal-involuntary
external-voluntary
In the large intestine, symmetrical segmentation dominates but is interrupted at infrequent intervals by a _____
regional propulsive mass movement
Requirements for defacation and swallowing (3)
- coordinated activity of striated muscle innervated by spinal nerves
- coordinates activity of smooth muscle innervated by ENS
- sensory nerves and ANS are required
Fecal continence requires the following: (5)
intact:
- internal and external anal sphincters
- pudental nerves –are sensory and also regulate external sphincter
- sacral autonomic nerves
- sacral spinal cord
- forebrain and corticospinal pathways
Regulation of defacation reflex
intrarectal pressure increases —> relax internal sphincter –> GVA to sacral cord and cortex –> constrict external sphincter –> decide what’s next –> if ok to defecate, use program in sacral cord (modulated by cortical centers)
