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38 Cards in this Set
- Front
- Back
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Innervation of the gut
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(1)extrinsic - parasympathetic
sympathetic (2)intrinsic - Enteric Nervous System myenteric plexus submucosal deep muscular plexus (3)Interstitial cells of Cajal |
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Smooth Muscle relaxing NTs
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NOS
calretinin VIP |
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smooth muscle contracting NTs
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ACh
NE |
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interstitial cells of cajal markers, properties, function
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establish gap junctions with smooth muscle and between each other
Express c-Kit signaling – receptor for Steele Factor Functions: pacemaker cells Or neuroregulators Five types: depends on where they are found |
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Phases of response to meal
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cephalic
gastric intestinal interdigestive |
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cephalic response to meal
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sight, smell, and taste of food, mechanical stimulation of oral cavity
Salivation – sitmulates cholinergic nerves Vagal reflexes inhibt contractile activity in proximal stomach (relaxes) Stimulate acid secretion |
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gastric phase response to meal
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neural but local mechanism
Food in stomach distends stomach Stimulates secretion of acid and enzymes Also reflexes stimulate preparation of small intestine for food |
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intestinal phase response to meal
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stomach empties into intestine
Most digestion occurs in small intestine Signals – stimulate secretion of enzymes (less motility) |
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interdigestive phase response to meal
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3-4 hours post food
Contractility wave – migratory motor complex Absorption and motility |
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cell structure of smooth muscles
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Arranged in bundles of functional units
Mechanically and electrically coupled Gap junctions electrically couple Collagen mechanically couples Intermediate filaments form dense bodies – anchoring proteins for contractile elements Dense bands – material on membranes, same function as dense bodies Caveolae – t- tubule like function Invaginations of membrane near sarcoplasmic reticulum |
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smooth muscle contraction
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Light chain is phosphorylated by MLCK allowing actin and myosin to interact
Phosphorylated myosin is hten capable of hydrolyzing ATP and binding Actin Calcium concentration allows for myosin phosphorylation Calcium channel – regulates flow of calcium in and out And a membrane channel Intracellular stores of calcium Contraction types Phasic – levels of calcium determine amount of force Tonic – triggered by calcium, but even if calcium levels decrease, force is maintained |
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rhythm of smooth muscle contraction
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Basal electrical rhythm (BER)
set by ICC spontaneous depolarization of slow waves when electrical signal reaches threshold, get mechanical contraction....requires environmental factors that promote threshold |
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types of motility
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(1)Peristalsis – esophagus, stomach, small intestine
Function is moving food (2)Rhythmic segmentation – small and large Mixing (3)Tonic – site of sphincters Block passage |
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stomach response to food
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(1)relaxation of the fundus
Vagal mediated NOS/VIP (2)food moves to corpus-antral Food is milled into chime (3)antral peristalsis emptying – spray chymes through pylori onto duodenum |
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solid vs liquid phase meal
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Solid vs liquid phase meal
Liquid – don’t require milling Faster empyting time No mixing |
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Gastric neuromuscular disorder
fundic accommodation |
(1) Fundic Accomodation – early satiety
Poor or excessive accommodation |
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gastric neuromuscular disorder
3 cpm electrical rhythm |
(2)3 cpm electrical rhythm – tachygastria, bradygastria
Nausea |
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gastric neuromuscular disorder
3 per min peristaltic contraction |
(3)3 per min Peristaltic contraction – hypomobility (grastroparesis)
Prolonged postprandial fullness |
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gastric neuromuscular disorder
antropylorodueodenal coordination |
(4) Antropyloroduodenal coordination – pylorospasm
Right upper quadrant pain |
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gastric neuromuscular disorder
normal vagal afferent activity |
(5) Normal Vagal Afferent Activity – hypersensitive stomach
nausea, pain, bloating |
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types of gastroparesis
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(1) Obstructive gastroparesis
(2) Ishcemic gastroparesis (3) Diabetic gastroparesis (4) Postsurgical gastroparesis (5) Miscellaneous causes – CVD, amyloid, MD (6) Idiopathic Gastroparesis – post viral, drug induced |
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normal small bowel motility
fasting vs fed |
Fasting –
Phase 1 – no contractions 10 min Phase 2 – increased, random contractions 70 min Phase 3 – migrating motor complex MMC 5-8 mins of strong antral-small bowel contractions that migrate to ileum every 90-100mins Fed – segmental and short duration peristaltic contractions |
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GI hormones
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Gastrin
CCK secretin GLP1 PYY ghrelin GIP motilin |
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stomach released hormones
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gastrin - g cell
somatostain - d cell |
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duodenum or jejunum released hormones
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secretin - S cell
CCK - i cell motilin - M cell GIP - k cell somatostain - d cell |
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ileum or colon released hormones
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GLP1 - L cell
PYY neurotensin somatostatin |
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Gastrin family hormones
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Gastrin - (1) glycine extended
(2)amide CCK - gastrin without sulfate group Receptors - CCK1 - gastrin CCK2 - cck |
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regulation of gastrin secretion
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secretion - gastric distention, protein digestion products
inhibitory - acid (h+) stimulates D cell that produces somatostatin that inhibits gastrin producing cells |
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Gastrin effects
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Gastrin directly stimulates parietal cell to make acid
Stimulates ECL cell that produces histamine which stimulates parietal cell to produce acid Stimulates D cell which produces somatostatin that inhibits acid production (and gastrin production) Amide type – cell proliferation in stomach and colon Differentiation of stomach cells Histamine secretion, acid secretion Acid secretion Glycine extended – colon proliferation and stomach differentiation Cell proliferation |
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CCK effects
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Effects – gall bladder contraction and relaxation of sphincter to release bile
Stimulates secretion of pancreatic enzymes Inhibits gastric emptying Growth promoting – pancreatic Langerhan cells Effects on pancreatic cells is mediated through the vagas CCK affects afferent vagals that send signal back through efferent vagals Gastric emptying effects – mediated through chylous lymph |
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Secretin family
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Secretin
VIP GIP Glucagon |
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secretin regulation
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hepatic bicarb secretion
Pancreatic bicarb secretion Inhibits gastric acid secretion Pancreatic growth |
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incretin hormones
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oral response to glucose higher than IV response
GIP GLP1 Function: inhibit glucagon secretion and decrease gastric emptying GIP – more important in insulin secretion GLP1 – potent agonist – used as therapy for diabetes GIP Stimulated for release by fatty acids, amino acids, glucose |
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motilin regulation and effects
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Secretion is increased in interdigestive period (fasting)
Comes in pulses Effect – increased contractility Receptor can be activated by some antibiotics erythromycin and roxithromycin Can cause diarrhea |
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appetite affecting hormones
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Appetite affecting hormones:
PYY – L cells in colon Ghrelin – X like endocrine cells in stomach Leptin – adipocytes |
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PYY
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PYY – suppresses appetite – induces satiety
Produced in colon Binds to Y2 receptor Secretion is inhibited by fasting |
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Ghrelin
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Ghrelin – related to motilin
Binds to specific receptor Secretion stimulated sharply before a meal and suppressed by ingestion Induces hunger sensation Also has effects on contractility |
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paracrine factors
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Paracrine Factors:
Somatostatin Histamine Nitric oxide – vasodilator but also relaxes sphincter Neural – vasodilator Paracrine – sphincter relaxer VIP Serotonin – Numerous receptor subtypes GRP |
