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14 Cards in this Set
- Front
- Back
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What are the two plexi of autonomic nerves in the wall of the GI tract? Where are they located? What do they regulate?
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Myenteric (Auerbach’s) plexus between the circular and
longitudinal muscle layers, Submucosal (Meissner’s) plexusis below the epithlelium. - secretion, fluid transport, vascular flow - motor control |
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What is the primary excitatory nt for motor neurons? inhibitory?
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ACh
NO (ATP, VIP, and PACAP contribute) |
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Where are the cells of Cajal found?
- respond to what? (3) - purpose? |
in the muscle layer
- NO, ACh, substance P - modulate neuronal signals to the smooth muscle of the gut |
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Control of tension in GI smooth muscle involves which 3 things?
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- Electromechanical coupling and contraction: depolarixation
- Hyperpolarization of smooth mus. membrane --> RELAXATION - Pharmacomechanical coupling: chemical stim from food |
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What do prokinetic agents do?
Are there more M2 or M3 muscarininc receptors in GI smooth muscle cells? What are carbachol and bethanechol? Are they widely used? Why or why not? |
enhance the coordinated motility and transit of
material in the GI tract. 4:1 M2 predom. muscarinic agonists no, b/c of SE and lack of efficacy |
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Do muscarinic agonists allow coordinated regulation of muscle contractility?
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No.
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What does neostigmine do?
Is it useful in cases of colonic psuedo-obstruction and paralytic ileus? |
inhibits degradation of Ach
Yes. |
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What effects does dopamine have on GI motility? Which receptors mediates these effects?
Do dopamine antagonists work as prokinetics? |
several inhibitory effects
- decreased GI motility is due to suppression of ACh release from myenteric motor neurons Dopamine --> Dopaminergic neuron --> synapses onto myenteric plexus SMC... releases dopamine --> inhibition D2R Not really. |
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What are Metoclopramide and domperidone?
- are they useful? - given in US? |
Dopamine antagonists
- not highly useful, no - not given here, but domperidone is used outside the US w/ modest success. |
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Which two 5HT receptors affect GI tract motility? Which is inhibitory/excitatory?
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5-HT3 & 4
- 3's are on inhibitory neurons; finding a way to inhibit this signaling would enhance motor responsiveness. - 4's are on excitatory neurons; agonists would *increase* GI motility. |
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What is the action of most currently available serotonin modulators (re: GI motility)?
Example? - is it a true prokinetic? - act primarily on upper GI or lower GI tract? - does it modulate the lower esophageal sphincter tone? antral and sm. intes contractions? - admin? - can act as a dopamine antagonist... what can this help? |
5-HT4 agonists.
Metoclopramide - yes - upper - increases it; stimulate them. - orally; used for increased gastric emptying - nausea/vomiting |
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What was Tegaserod (Zelnorm)?
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5HT4 agonist; withdrawn from the market last year due to increased
cardiovascular risk |
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What is Octreotide (Sandostatin)?
- accel/decel gastric emptying? - does it modulate release of hormones related to severe GI distress related to rapid passage of food into the small intestine? |
long acting somatostatin analog
- accelerate - yes, it inhibits their release. |
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What is the motilin receptor? Which antibiotic is an agonist? Non-antiB agonist?
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Motilin is a strong prokinetic (contractile) hormone with motilin receptors expressed
on smooth muscle cells - erythromycin - MotilinR |
