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25 Cards in this Set
- Front
- Back
What are the two basic structural subdivisions found throughout the GI tract? What are the functions of each?
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*mucosal layer: absorption and secretion
*muscular layer: movement of contents |
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What are the two layers of the muscular layer? What action does each have on the size of the GI tract?
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*outer longitudinal layer - shortens the length of the tube
*inner circular layer - constricts the diameter of the lumen |
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What is the primary blood supply of the GI system? What percentage of cardiac output is consummed by the GI tract during a meal? During flight-or-fight?
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*splanchnic circulation
*65% during a meal; 0% during flight-or-fight |
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What is the role of parasympathetic innervation in control of GI function? Sympathetic innervation? How is different from the innervation of the CV system?
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*parasympathetic is stimulatory
*sympathetic is inhibitory *this is the opposite of innervation of the CV system |
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Describe the effect of parasympathetic and sympathetic innervation of motility, secretion, and sphincter and vasculature tone in the GI tract.
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*parasympathetic innervation increases motility, increases secretion, relaxes sphincters, and dilates vasculature
*sympathetic inervation has the opposite effects |
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What are two reflexes controlled by motor programs.
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The swallowing and peristaltic reflexes.
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Where are the myenteric and submucosal plexuses located?
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The myenteric plexus is between the layers of the muscular layer and the submucosal plexus is found between the submucosa and the inner muscular layer.
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The movement of what ion controls the contraction of smooth muscle cells in the GI system?
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Ca++
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What are interstitial cells of Cajal? What is their function?
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They are the pacemaker cells of the GI tract that resemble a cross between a smooth muscle cell and a fibroblast. They generate driving potentials which stimulate slow wave potentials in smooth muscle cells.
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How are ICC connected to smooth muscle cells?
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Through gap junctions.
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How do GI smooth muscle cells repolarize (i.e. return to RMP)?
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Ca++ stimulates K+ channels to open which allows an efflux of this ion and repolarization of the cell.
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Is the rate of basal oscillation of GI smooth muscle cells constant throughout the tract? Why or why not?
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It is not - there is a gradient from 14/min in the duodenum to 7/min in the ileum. It is thought that this gradient propels lumenal contents in one direction.
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What is the action of ACh on smooth muscle cells?
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*it depolarizes them, bringing them above threshold potential and allowing voltage-gated Ca++ channels to open and cause "fast" action potentials
*inhibits K+ channels to prevent repolarization *stimulates synthesis of IP3 |
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What is the action of VIP on smooth muscle cells?
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*hyperpolarizes cell
*activates K+ channels which induces repolarization *induces cAMP production which lowers [Ca++] *decreases pacemaker frequency |
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What initiates the peristaltic reflex?
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Food in the lumen stimulates mechanoreceptors which release serotonin, which in turn stimulates interneurons in the submucosal plexus.
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What are the end actions of the peristaltic reflex?
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*mucus release is stimulated in front of the bolus
*ACh stimulates muscular contraction behind the bolus *VIP and NO induce muscular relaxation in front of the bolus |
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Describe the smooth muscle action seen in W/Wv mice.
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These mice lack ICC and their smooth muscle cells show erratic Ca++ dependent potentials. There are random contractions, but no organized waves. As a result, food moves much more slowly.
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What type of symptoms are seen in humans who have defective ICC or lack them altogether?
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Low motility resulting in constipative disease.
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What are two specific mechanisms of mucosal immunity in the GI tract?
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*M cells pick up and present antigen
*production of secretory IgA by B-cells |
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How is the pacemaking seen in the GI system different from that of the cardiovascular system?
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In the cardiovascular system, pacemaking is focal, rapid, and nearly synchronous. In the gut it is distributed, slow, and variable in time and space.
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Are driver potentials produced by ICC due to the movement of Ca++, Na+, or K+?
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They are initiated by the opening of a channel that doesn't discriminate between Na+ or K+. Ca++ does not seem to be involved as the cells continue to generate potentials even when a Ca++ channel blocker is applied.
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How do excitatory motor neurons in the myenteric plexus stimulate smooth muscle cells of the muscular layer?
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They release ACh which has a variety of stimulatory effects on the smooth muscle cells.
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How do signals from excitatory motor neurons affect the slow wave potentials generated by smooth muscle cells in the gut?
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They increase the amplitude and duration of the slow wave potentials which causes the muscle to contract rhythmically. Also, ACh allows the generation of fast potentials.
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How do inhibitory motor neurons affect the slow wave potentials of smooth muscle cells in the gut?
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They decrease the amplitude, duration, and frequency of the slow wave potentials which causes the muscle to relax.
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How do inhibitory motor neurons exert their effect on smooth muscle cells?
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They release VIP which has a variety of inhibitory effects.
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