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46 Cards in this Set
- Front
- Back
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layers of the intestinal wall outer to inward |
1) serosa 2) longitudinal muscle 3) circular muscle 4) submucosa 5) mucosa |
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slow waves of electrical activity |
not via Aps, undulating changes in the resting membrane potential |
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intensity and frequency of slow waves |
varies btwn 5 and 15 mV and 3-12 per minute |
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interstitial cells of Cajal |
electrical pacemakers for smooth muscle - excite appearance of intermittent spike potentials which in turn excites muscle contraction |
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spike potential AP set point |
~-40 mV (normal gut resting potential ~-50 to -60) |
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how long do GI spikes last |
10-20 milliseconds (10-40 longer than large nerve fibers) |
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what accounts for the long-lasting APs in GI tract |
slow calcium-sodium channels allowing lage amount to Ca2+ and smaller amounts of Na+ into cell |
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factors that depolarize the membrane in GI tract smooth muscle |
1) stretching of muscle 2) acetylcholine stimulation 3) parasympathetic nerve stimulation 4) stimulation by several specific GI hormones |
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factors that hyperpolarize the membrane of GI tract smooth muscle |
1) norepi and epi 2) stimulation by sympathetic nerves |
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what do the Ca2+ entering GI smooth muscle activate |
myosin filaments via a calmodulin control mechanism |
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what enters smooth muscle during slow waves |
sodium |
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what is tonic contraction of GI smooth muscle sometimes caused by |
repetative spike potentials, hormones or other factors, entery of Ca2+ without membrane potential change |
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outer plexus btwn the longitudinal and circular muscle layers |
myenteric plexus/ Auerbach's plexus |
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inner plexus in the submucosa |
submucosal/Meissner's plexus |
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effects of stimulating the myenteric plexus |
1) increased tonic tone 2) increased intensity of rhythmical contractions 3) increased rate of contractions 4) increased velocity of conduction excitatory waves |
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inhibitory neurons in myenteric plexus secrete |
vasoactive intestinal polypeptide - inhibit intestinal sphincter muscles that impede movement of food (pyloric, ilioceceal valve) |
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what is the submucosal plexus concerned with |
local intestinal secretion, absorption, and contraction of submucosal muscle |
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what does contration of submucosal muscle cause |
various degrees of infolding of Gi mucosa |
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where do sacral parasympathetics arise |
S2-4 |
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where do sympathetic fibers to the GI tract originate |
T5-L2 |
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distribution of parasympathetics vs sympathetics throughout GI tract |
parasympathetics have move fibers in oral cavity and anus areas, sympathetics have even distribution |
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how does sympathtic activation affecct Gi tract |
1) some direct muscle iinhibition 2) mostly via inhibition of entire enteric nervous system |
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refelxes integrated wntirely within the gut wall enteric nervous system |
secretion, peristalsis, mixing contractions, local inhibitory effects, etc |
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refelxes from gut to prevertebral sympathetic ganglia and then back into GI tract |
gastrocolic reflex, enterogastrc reflexes, colonoileal reflex |
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gastrocolic reflex |
signals from stomach cause evacuation of colon |
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enterogastic reflex |
signals from colon and small intestine to inhibit motility of stomach and stomach secretion |
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colonoileal reflex |
colon inhibit emptying of ileal contents into colon |
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reflexes from the gut to spinal cord/brain and back to GI tract |
vagus nerve control, pain reflexes, defecation reflexes |
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what secretes gastrin |
G cells of the antrum of the stomach in response to stimuli like stomach distention, products of proteins, and gatrin releasing peptide |
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what releases gastrin releasing peptide |
nerves of gastric mucosa during vagal stimulation |
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actions of gastrin |
1) stimulation of gastric acid secretion 2) stimulation of growth of gastric mucosa |
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what secretes cholecystokinin |
I cells in mucosa of duodenum and jejunum in response to products of fat, fatty acids, and monglycerides |
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action of cholecystokinin |
strongly contracts galbladder, inhibits stomach contraction moderately |
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what secretes secretin |
S cells in mucosa of duodenum in response to acidic gastric juice |
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secretin action |
mild effect on motility of GI tract and acts to promote pancreatic secretion of bicarb |
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what secretes gastric inhibitory peptide |
mucosa of upper small intestine in response to fatty and amino acids and somewhat to carbs |
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gastric inhibitory peptide action |
mildly decreases motor activity of stomach |
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what secretes motilin |
upper duodenum during fasting |
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motilin action |
increase gastric motility; waves released every 90 minutes in fasting person |
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usual stimulus for intestinal peristalsis |
distention of the gut |
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receptive relaxation aka myenteric/peristaltic reflex |
gut sometimes relaxes several cm downstream toward anus allowing food to be propelled more easily anally than orad |
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how long are local intermittent constritive contractions tha allow mixing |
5 to 30 seconds |
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splanchnic circulation |
GI, spleen, pancreas, and liver |
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vasodilator substances released during digestion |
kallidin and bradykinin are main ones along with decreased O2; also cholecystokinin, vasoactive intestinal peptide, gastrin, secretin, |
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what occurs due to the villi structure of arterioles and venules |
blood oxygen diffuses out of arterioles directly into venules without being carried to the tips of the villi (up to 80% of the oxygen takes this route) |
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how much blood can sympathetic stimulation shunt away from GI in times of hemorrhagic shock |
200-400 ml |
