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43 Cards in this Set
- Front
- Back
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After completing this lecture students should be able to
Identify the major organs of the GI system and their principal functions Describe the established GI hormones, their sites of secretion, their important physiological functions, and the stimuli that regulate their release Identify the components of the enteric (intrinsic) nervous system, their role in neural control of GI function, and their relation to the extrinsic innervation of the GI tract Describe the primary effects of sympathetic and parasympathetic stimulation on GI motility and secretory activity Identify key disorders associated with the GI system malfunction |
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Obesity is
a) Pandemic b) Endemic c) Epidemic |
a) Pandemic
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__________ cancer - 2nd deadliest cancer in US
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Colorectal cancer - 2nd deadliest cancer in US
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_______ is the 3rd leading cause of death worldwide
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Diarrhea is the 3rd leading cause of death worldwide
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GI hormones:
S______ G______ C_____________________ G_____ I_________ Peptide (GIP) M______ |
GI hormones:
Secretin Gastrin Cholecystokinin (CCK) Gastric Inhibitory Peptide (GIP) Motilin |
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VIP = V________ I_________ P______
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VIP = Vasoactive Intestinal Peptide
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Gastrin's half-life is dependent on ____
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Gastrin's half-life is dependent on size
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_______ and ___
- 5 C-terminal AA identical - Produce all effects of each other at high doses |
Gastrin and CCK
- 5 C-terminal AA identical - Produce all effects of each other at high doses |
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S_______, GIP, VIP, g______
- some effects are shared |
Secretin, GIP, VIP, glucagon
- some effects are shared |
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Gastrin Release
Released from _ cells in antrum (90%) and duodenum (10%) Stimuli - protein digestion products - nervous, physical distention - (c_____, decaf coffee, and w_____) Inhibition - a__________ of antrum |
Gastrin Release
Released from G cells in antrum (90%) and duodenum (10%) Stimuli - protein digestion products - nervous, physical distention - (calcium, decaf coffee, and wine) Inhibition - acidification of antrum |
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Gastrin Response to meal
Large amounts of G-17 released from a_____ (digestion phase) Small amounts of G-34 released from d_______ (interdigestive phase-fasting) |
Gastrin Response to meal
Large amounts of G-17 released from antrum (digestion phase) Small amounts of G-34 released from duodenum (interdigestive phase-fasting) |
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Gastric acid secretion
1,500x more potent than h_________ |
Gastric acid secretion
1,500x more potent than histamine |
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Gastrin Trophic activity
Stimulates growth of o_____ mucosa of stomach, duodenal mucosa, and colon mucosa Surgical removal of a______ causes atrophy Patients with gastrin secreting tumors have m_______ hyperplasia and hypertrophy |
Gastrin Trophic activity
Stimulates growth of oxyntic mucosa of stomach, duodenal mucosa, and colon mucosa Surgical removal of antrum causes atrophy Patients with gastrin secreting tumors have mucosal hyperplasia and hypertrophy |
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Gastrinoma - _____________ syndrome
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Gastrinoma - Zollinger-Ellison syndrome
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Gastrinoma - Zollinger-Ellison syndrome
Gastrin secreting tumor Non-beta cell tumor of pancreas (80%) or G-cell tumors in d_______ (10-15%) Continually secretes gastrin into blood Hypergastrinemia causes hypersecretion of acid Increased p________ cell mass Constant stimulation of hyperplastic m_____ Symptoms Duodenal ulcers, ___rrhea, ________rrhea, ____kalemia |
Gastrinoma - Zollinger-Ellison syndrome
Gastrin secreting tumor Non-beta cell tumor of pancreas (80%) or G-cell tumors in duodenum (10-15%) Continually secretes gastrin into blood Hypergastrinemia causes hypersecretion of acid Increased parietal cell mass Constant stimulation of hyperplastic mucosa Symptoms Duodenal ulcers, diarrhea, steatorrhea, hypokalemia |
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Cholecystokinin
Biological activity - Minimal active fragment - 7 C-terminal AA T______, 7 residues from C-terminal must be s_______ for full activity at physiological levels Produces all effects of g______ at high doses |
Cholecystokinin
Biological activity - Minimal active fragment - 7 C-terminal AA Tyrosine, 7 residues from C-terminal must be sulfated for full activity at physiological levels Produces all effects of gastrin at high doses |
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CCK
Released from _-cells in duodenum and j______ Stimuli for release Fatty acids or ____glycerides (not triglycerides) peptides and single AA Acid (weak) Half-life of 5-7 minutes Cleared from circulation by kidneys or liver (CCK_) |
CCK
Released from I-cells in duodenum and jejunum Stimuli for release Fatty acids or monoglycerides (not triglycerides) peptides and single AA Acid (weak) Half-life of 5-7 minutes Cleared from circulation by kidneys or liver (CCK8) |
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CCK
Pancreatic exocrine Potent stimulator of enzyme secretion (pancreatic fluid) Weak stimulator of b_________ secretion (but can potentiate s______ effects) Emptying of gallbladder contracts gallbladder (smooth muscle contraction) and relaxes sphincter of Oddi I_______ gastric emptying Trophic effects - exocrine pancreas and gallbladder mucosa Increase pancreatic DNA, RNA and protein content |
Pancreatic exocrine
Potent stimulator of enzyme secretion (pancreatic fluid) Weak stimulator of bicarbonate secretion (but can potentiate secretin effects) Emptying of gallbladder contracts gallbladder (smooth muscle contraction) and relaxes sphincter of Oddi Inhibits gastric emptying Trophic effects - exocrine pancreas and gallbladder mucosa Increase pancreatic DNA, RNA and protein content |
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Secretin
Biological activity – No active fragments - entire molecule is required Active form is -helix - tertiary structure requires all AA Removed from circulation by ______ Half-life of 4 minutes |
Secretin
Biological activity – No active fragments - entire molecule is required Active form is -helix - tertiary structure requires all AA Removed from circulation by kidneys Half-life of 4 minutes |
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Secretin
Released from _-cells of duodenal mucosa Stimuli for release ____ in duodenum (pH <4.5) Fatty acids in duodenum Physiological effects - “Nature’s Antiacid” Inhibits _______ acid secretion (enterogastrone) Stimulates pancreatic and bile b_______ secretion Stimulates p_____ secretion Trophic effect on exocrine pancreas Stimulates pancreatic acid secretion and insulin release, and gallbladder contraction I______ gastric emptying, gastric and intestinal motility and mucosal growth |
Secretin
Released from S-cells of duodenal mucosa Stimuli for release Acid in duodenum (pH <4.5) Fatty acids in duodenum Physiological effects - “Nature’s Antiacid” Inhibits gastric acid secretion (enterogastrone) Stimulates pancreatic and bile bicarbonate secretion Stimulates pepsin secretion Trophic effect on exocrine pancreas Stimulates pancreatic acid secretion and insulin release, and gallbladder contraction Inhibits gastric emptying, gastric and intestinal motility and mucosal growth |
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Gastric Inhibitory Peptide (GIP)
Stimuli / release Released _-cells from duodenum and proximal jejunum All major foodstuffs - fat must be hydrolyzed Oral glucose but not ____ glucose Half-life of 20 minutes Cleared by _______ |
Gastric Inhibitory Peptide (GIP)
Stimuli / release Released K-cells from duodenum and proximal jejunum All major foodstuffs - fat must be hydrolyzed Oral glucose but not i.v. glucose Half-life of 20 minutes Cleared by kidneys |
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Gastric Inhibitory Peptide (GIP)
Physiological effects - Stimulates i______ release (also called glucose-dependent insulinotrophic peptide - GIP) Inhibits ______ acid secretion or intestinal m_______ (enterogastrone) |
Gastric Inhibitory Peptide (GIP)
Physiological effects - Stimulates insulin release (also called glucose-dependent insulinotrophic peptide - GIP) Inhibits gastric acid secretion or intestinal motility (enterogastrone) |
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Motilin
Stimuli/release - Released from duodenum and proximal jejunum during fasting at ___ min intervals Release is under n______ control Half-life of 4.5 minutes and catabolized by kidney Physiological effects - S_________ upper G.I. motility Accounts for the migrating motility complex, "h____________ contractions” – wave of contraction that sweeps the length of the gut. |
Motilin
Stimuli/release - Released from duodenum and proximal jejunum during fasting at 100 min intervals Release is under neural control Half-life of 4.5 minutes and catabolized by kidney Physiological effects - Stimulates upper G.I. motility Accounts for the migrating motility complex, “housekeeping contractions” – wave of contraction that sweeps the length of the gut. |
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Paracrines:
Somatostatin (peptide) Found in gastric / duodenal mucosa and pancreas Release - stimulated by ____, inhibited by ___ I_______ release of all gut hormones Directly inhibits ______ cell acid secretion Mediates acid induced inhibition of _______ release |
Paracrines:
Somatostatin (peptide) Found in gastric / duodenal mucosa and pancreas Release - stimulated by acid, inhibited by Ach Inhibits release of all gut hormones Directly inhibits parietal cell acid secretion Mediates acid induced inhibition of gastrin release |
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Paracrines
Histamine Gastrin and Ach cause release from cells in stomach Stimulates ____ secretion Histamine H2 receptor blockers --> decreases Acid secretion C________ (Tagamet), R_________ (Zantac) |
Paracrines
Histamine Gastrin and Ach cause release from cells in stomach Stimulates acid secretion Histamine H2 receptor blockers Acid secretion Cimetidine (Tagamet), Ranitidine (Zantac) |
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Neurocrines
VIP' action is _________ __ _____ ___ |
Neurocrines
VIP' action is Relaxation of gut SM |
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Neurocrines
GRP (Bombesin)'s action is ______ _______ ______ |
Neurocrines
GRP (Bombesin)'s action is increase Gastrin Release |
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Neurocrines
Enkephalins action is _________ ___ ____ |
Neurocrines
Enkephalins action is Increase SM tone |
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Myenteric Plexus
Location - Esophagus to anus Between l________ and c________ __ layers |
Myenteric Plexus
Location - Esophagus to anus Between longitudinal and circular SM layers |
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Submucosal Plexus
Function - Local control Secretion Absorption Contraction of __________ _______ |
Submucosal Plexus
Function - Local control Secretion Absorption Contraction of muscularis mucosa |
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Sympathetic Innervation
Preganglionic Neurons (long) - Originate at __-__ (cell bodies). Synapse in prevertebral ganglia Postganglionic Neurons (long) Originate in ganglia (cell bodies) Innervate entire gut. Terminate in ENS (mostly) Inhibitory influences (mostly) by (a) decreasing activity of ENS. (b) Direct effect to inhibit SM Sympathetic nerves also contain afferent sensory fibers (50%) |
Sympathetic Innervation
Preganglionic Neurons (long) - Originate at T5-L2 (cell bodies). Synapse in prevertebral ganglia Postganglionic Neurons (long) Originate in ganglia (cell bodies) Innervate entire gut. Terminate in ENS (mostly) Inhibitory influences (mostly) by (a) decreasing activity of ENS. (b) Direct effect to inhibit SM Sympathetic nerves also contain afferent sensory fibers (50%) |
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Parasympathetic Innervation:
Cranial Division - (V_____ N.) - first half of gut Sacral Division - (P_____ N.) - second half of gut Neurons - preganglionic - long - postganglionic - short, entirely in ENS. Synapse mainly with ENS neurons S__________ - excites ENS (in general) Parasympathetic nerves also contain afferent sensory fibers (80%) |
Parasympathetic Innervation:
Cranial Division - (Vagus N.) - first half of gut Sacral Division - (Pelvic N.) - second half of gut Neurons - preganglionic - long - postganglionic - short, entirely in ENS. Synapse mainly with ENS neurons Stimulation - excites ENS (in general) Parasympathetic nerves also contain afferent sensory fibers (80%) |
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Neurotransmitters (Neurocrines)
Preganglionic efferent neurons - ___ Postganglionic efferent neurons PNS - ___________ SNS - _____________ Enteric nervous system (many others) Excitatory - __________, _________ P Inhibitory - ___, __ |
Neurotransmitters (Neurocrines)
Preganglionic efferent neurons - ACh Postganglionic efferent neurons PNS - acetylcholine SNS - norepinephrine Enteric nervous system (many others) Excitatory - acetylcholine, substance P Inhibitory - VIP, NO |
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GI Refelxes:
Long loop Gut --> Aff. N. --? prevertebral ganglia --> Eff. N. --> gut Reflexes: gastrocolic, enterogastric, colonoileal |
GI Refelxes:
Long loop Gut --> Aff. N. --? prevertebral ganglia --> Eff. N. --> gut Reflexes: gastrocolic, ? enterogastric, ? colonoileal ? |
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Gastrointestinal Reflexes:
Vagovagal Reflexes Stomach / duodenum --> Aff. N. --> brain stem --> Eff. N. --? stomach / duodenum Controls gastric motor and secretory activity |
Gastrointestinal Reflexes:
Vagovagal Reflexes Stomach / duodenum --> Aff. N. --> _____ ____ --> Eff. N. --? stomach / duodenum Controls gastric motor and secretory activity |
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GI reflexes:
Defecation Reflexes Colon/rectum --> Aff. N. --> ____ ___ --> Eff. N. --> colon /rectum |
Defecation Reflexes
Colon/rectum Aff. N. spinal cord Eff. N. colon /rectum |
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Unitary (single unit) Smooth Muscle
Functions as a s_________ S________ - nucleated mass of protoplasm produced by merging of cells Large areas of SM contract as single unit ___ Junctions Low resistance pathways for ion movement Between bundles of cells and layers of SM Signal propagation - AP spreads from cell to cell Within and between muscle layers |
Unitary (single unit) Smooth Muscle
Functions as a syncytium Syncytium - nucleated mass of protoplasm produced by merging of cells Large areas of SM contract as single unit Gap Junctions Low resistance pathways for ion movement Between bundles of cells and layers of SM Signal propagation - AP spreads from cell to cell Within and between muscle layers |
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Slow Waves
Rhythmical changes in membrane potential caused by variations in _______ conductance Fixed frequency - Interstitial cells of _____ - pacemaker cells Dictates max. frequency of SM contraction Independent of nervous / hormonal stimuli Variable amplitude - Affected by nervous / hormonal stimuli Increased amplitude --> Incr in spike potential frequency --> incr in strength of contraction |
Slow Waves
Rhythmical changes in membrane potential caused by variations in sodium conductance Fixed frequency - Interstitial cells of Cajal - pacemaker cells Dictates max. frequency of SM contraction Independent of nervous / hormonal stimuli Variable amplitude - Affected by nervous / hormonal stimuli Increased amplitude --> Incr in spike potential frequency --> incr in strength of contraction |
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Spike Potentials
True action potentials Occur when slow waves reach threshold (-__ mV) Cause SM contraction Voltage dependent calcium channels Ca++ entry --> c__________ Frequency Affected by nervous / hormonal stimuli Incr frequency --> stronger contraction Incr frequency does not Incr max. ________ of contraction |
Spike Potentials
True action potentials Occur when slow waves reach threshold (-40 mV) Cause SM contraction Voltage dependent calcium channels Ca++ entry --> contraction Frequency Affected by nervous / hormonal stimuli Incr frequency --> stronger contraction Incr frequency does not Incr max. frequency of contraction |
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Propulsive Movements - Peristalsis
Stimuli that initiate peristalsis D__________ - orad contraction with downstream receptive relaxation = “___ of the Gut” I_________ of gut epithelium P____________ nervous system Function Myenteric plexus required Atropine (blocks ACh receptors) - Decr peristalsis Congenital absence of plexus - no peristalsis |
Propulsive Movements - Peristalsis
Stimuli that initiate peristalsis Distention - orad contraction with downstream receptive relaxation = “Law of the Gut” Irritation of gut epithelium Parasympathetic nervous system Function Myenteric plexus required Atropine (blocks ACh receptors) - Decr peristalsis Congenital absence of plexus - no peristalsis |
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The Splanchnic Circulation
Components - GI tract, spleen, pancreas, and liver Feed Arteries (25-30% CO) ________ artery - stomach, spleen ___. Mesen. A. - S.I., pancreas, prox. colon ___. Mesen. A. - majority of colon Venous drainage Portal vein --> liver sinusoids --> hepatic vein Reticuloendothelial cells remove bacteria 1/2 to 1/3 nutrients removed and stored in liver |
The Splanchnic Circulation
Components - GI tract, spleen, pancreas, and liver Feed Arteries (25-30% CO) Celiac artery - stomach, spleen Sup. Mesen. A. - S.I., pancreas, prox. colon Inf. Mesen. A. - majority of colon Venous drainage Portal vein --> liver sinusoids --> hepatic vein Reticuloendothelial cells remove bacteria 1/2 to 1/3 nutrients removed and stored in liver |
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Control of Gut Blood Flow
Blood flow proportional to local activity Meal --> Incr blood flow (2-3 fold) for 3-6 hr Causes of activity-induced blood flow Vasodilator hormones - g_____, s_______, ___ Vasodilator kinins Low oxygen (high adenosine) Nervous control of blood flow PNS - Incr gut activity --> Incr blood flow SNS - Directly decr blood flow - Autoregulatory escape, exercise, shock |
Control of Gut Blood Flow
Blood flow proportional to local activity Meal --> Incr blood flow (2-3 fold) for 3-6 hr Causes of activity-induced blood flow Vasodilator hormones - gastrin, secretin, CCK Vasodilator kinins Low oxygen (high adenosine) Nervous control of blood flow PNS - Incr gut activity --> Incr blood flow SNS - Directly decr blood flow - Autoregulatory escape, exercise, shock |
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Countercurrent Oxygen Loss
Normal conditions __% oxygen is shunted from artery to vein Not harmful Circulatory Shock / decreased cardiac output / hypotension / mechanical obstruction Splanchnic blood flow greatly reduced V_______ tip or entire v______ suffers ischemic death Absorptive capabilities diminished |
Countercurrent Oxygen Loss
Normal conditions 80% oxygen is shunted from artery to vein Not harmful Circulatory Shock / decreased cardiac output / hypotension / mechanical obstruction Splanchnic blood flow greatly reduced Villus tip or entire villus suffers ischemic death Absorptive capabilities diminished |
