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63 Cards in this Set

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Factors that control resting membrane potential. Do these agents hyperpolarize or depolarize:
1. Norepinephrin
2. Secretin
3. Stretch
4. CCK
5. Acetycholine
6. SNS
7. PNS
8. Motilin
1. Norepinephrin - H
2. Secretin - H
3. Stretch - D
4. CCK - H
5. Acetycholine - H
6. SNS - H
7. PNS - D
8. Motilin - D
Acetycholine is excitatory or inhibitory?
What about norepienphrin/epinephrin?
1. Acetylcholine = Excitatory
2. Norepi = inhibitory
Describe the path of the affarent fibers from the ENS to the brainstem (p585)
1. Cell bodies in ENS to
2. Axons terminate in prevertebral sympathetic ganglia (celia, mesenteric hypogastric) to
3. Cell bodies in dorsal root ganglia of cord or cranial nerve to
4. gut signals to cord or medulla
What is the Vagovagal reflex? p586
Vagal sensory nerves relay stretch information to the brainstem, releasing vagal efferents to parietal and G cells in stomach.
What are the two divisions of the Parasympathetic system? What about the Sympathetic Division? (what is the range in Spinal Cord)?
Cranial and Sacral (2-4th sacral segments)
Sympathetic = T5-L2
Define Gastrocolic reflex:
Enterogastric:
Colonoileal:
1. Gastrocolic: evacuation of colon with stomach filling
2. Stomach motility/secretion inhibition with intestinal filling
3. Inibition of ileal motility with colon filling.
How does secretin affect the GI motility? What is it secreted by?
Mild inhibitor. Secreted by S cells of duodenal mucosa in response to acidic contents entering pylorus.
How does GIP affect the GI? What is it secreted by and in response to what?
Decreases stomach motility, slows emptying into small intestine. Secreted by mucosa of upper small intestine in response to fatty acids, amino acids, CHO.
What is achalasia?
The failure of Gastroesophagel caudal to bolus to receptively relax. Causes severe megaesophagus.
How does CCK work to increase motility? Where is CCK secreted?
It is secreted from jejunal mucosa and it acts to block effects of gastrin to increase motility.
How does the effect of gastrin, CCK, insulin, and serotonin differ in the intestine compared to the stomach?
These hormones increase motility in the intestine but slow the stomach.
What compounds inhibit intestinal motility?
Secretin, glucagon, GIP, VIP
What part of the nervous system initiates peristaltic rush?
ANS and ENS
What constitutes the ENS?
Meissner's (submucosal) and Auerbach's (myenteric) plexuses plus other neurons of the GI tract
A neural or hormonal stimulus will cause extrusion of vesicle contents - what is the mechanism?
Signal increases Ca2+, it enters the cell, causes vesicle fusion with membrane
What is counterintuitive with respect to the sympathetic NS and the way it affects glands? (p607)
Stimulation by SNS increases secretion from local glands but it also causes vasoconstriction to perfusing vessels and in effect, secretion does not have much of an effect.
In saliva, what are the two major ions secreted? What are the major primary secretions?
K+ and HCO3-; NaCl, CFTR, Cl- channels
Due to the greater Na reabsorption compared to K in saliva secretion, what happens?
Electronegativity that's created causes Cl- to be passively reabsorbed.
What does bradykinin do?
It's a vasodilator that increases blood flow and nutritive absorption in the GI
Type of gland found at both ends of the esophagus?
Mucus
What do Oxyntic Glands secrete? Where are they found in the stomach?
HCl, Pepsinogen, Intrinsic factor (for VitK absorption) and mucus. Found in the proximal 80% of the stomach.
What do pyloric glands secrete? Where are they found?
Secrete mucus, pepsinogen and gastrin. Found in distal 20% of stomach lining.
How is pepsinogen stimulated for release? What is the stimulation in response to? How is pepsinogen activated?
Stimulated by peptic cells by Ach from vagus nerves or gastric ENS. Peptic cells respond to stomach acid and pepsinogen is activated when exposed to HCl in the presence of pepsin.
What does pepsin degrade?
Proteins and hydrolyzes collagen.
What are the three types of oxyntic glands? And what do they secrete?
1. Mucus neck cell (secretes mucus and pepsinogen)
2. Peptic (chief) cells secrete pepsinogen
3. Parietall (oxyntic) cells secrete hydrochloric acid
How is HCl produced?
CO2 enters cell and CA catalyzes reaction with water to make H+ and HCO3-. The HCO3- is pumped into interstitial space in exchange for Cl-. The H+ is pumped into lumen in exchange for K and Cl is excreted via Cl channel.
What conditions do Pepsin require for proper function?
Acidic environment.
What is pernicious anemia and what prevents it?
Failed maturation of erythrocytes. Intrinsic factor not being produced by parietal cells causes it.
What do pyloric glands produce?
Small amount of pepsinogen and large quantities of mucus.
What neurotransmitters and hormones activate secretion?
Ach, gastrin, histamine
What hormones predominanltly activate acid secretion by parietal glands? p613
Histamine and Gastrin
What neurotransmitter activates all types of secretion in gastric glands (pepsinogen, hydrochloric acid, mucus?)
Ach
What two factors control HCl secretion?
Endocrine and nervous control
These cells secrete this substance directly onto parietal cells to secrete HCl
Enterochromaffin cells secrete histamine
Parietal cells secrete this substance in response to meat proteins and other foods?
Gastrin
What hormone stimulates acid secretion in the distal stomach? It also stimulates these cells to produce this.
Gastrin - it also stimulates chromaffin cells to secrete histamine.
What is secreted by D cells
Somatostatin p615
When the cephalic phase is active, what NS does it excite and cause the release of?
Parasympathetics that stimulate pepsin and acid production
What happens during the gastric phase?
1. Local nervous secretory reflexes
2. Vagal reflex
3. Gastrin stimulation
What happens in the intestinal phase?
1. Nervous mechanisms
2. Hormonal mechanisms
What triggers secretion by the pancreas?
Chyme in the duodenum
How does the pancreas produce/secrete HCO3 into the lumen?
CO2 diffuses into ductule cell from the blood; CA converts it to HCO3; Na is actively transported into the ductule via the blood; NaHCO3 is actively transported into the lumen.
What enzyme is used to digest CHO? What does it degrade CHO to?
Pancreatic amylase. Degrades it to di- and tri-saccharides
What enzyme is used to digest Fats? (3)
Pancreatic lipase; cholesterol esterase; phospholipase
What are the proteolytic enzymes secreted by the pancreas?
Trypsin/chymotrypsin (smaller aa); carboxypolypeptidase (to individual aa)
How is trypsin activated?
The presence of chyme induces secretion of enterokinase.
Trypsin is activated by enterokinase but how are the others activated?
Once trypsin is activated, it cleaves the other pro-enzymes into their active forms.
What are the three main stimuli of pancreatic secretion?
1. Acetycholine
2. Cholecystokinin
3. Secretin
1. Acetycholine
2. Cholecystokinin
3. Secretin
These are involved in stimulating the pancreas. Where does each function?
1. Acetycholine - acini
2. Cholecystokinin - acini
3. Secretin - ducts
What type of cells produce cholecystokinin? What mucosa produces it?
I cells. Produced by duodenal/jejunal mucosa)
Describe how the phases of pancreatic secretion are influenced by the cephalic, gastric and intestinal phase.
1. Cephalic phase causes Ach to stimulate acini to release moderate amounts of enzymes (~20%). But low flow
2. Gastric Phase. Continuance of cephalic phase adds about 10% total. Still low flow
3. Intestinal phase - when chyme enters duodenum, secretin and CCK are released causing copious release of pancreatic secretions
What is the "multiplicative" concept?
When Ach, CCK, and Secretin are all secreted together, the combined effect is greater than alone.
The bile ducts secrete weak NaHCO3 to help in acid neutralization. What stimulates this release?
Secretin
Where is most of the bile acid reabsorbed for recycling?
Distal ileum
What are the four components of bile?
1. Bile acids
2. Phospholipids
3. Cholesterol
4. Bile pigments
What stimulates gall bladder contraction? Why does component that stimulates contraction make sense?
Release of CCK. CCK is secreted more if there is high fat. If high fat, then there is higher need for bile acids
[this is similar to earlier note card but for completeness...] What two things stimulate bile release?
1. CCK - that causes constriction of the bile duct and relaxation of Vader
2. Stimulation by ACh
The amount of cholesterol in bile is a function of:
Dietary fat and fat metabolism in the liver
What glands secrete a lot of mucus in the duodenum?
Brunner's Glands
What three things stimulate Brunner's Glands in the duodenem?
1. Tactile/irritating stimuli of mucosa
2. Vagal stimulation (increased secretion with increased stomach secretion)
3. GI tract hormones, especially secretin
The crypts of Lieberkuhn are covered by an epitheium composed of these two types of cells (what do they secrete?)
1. Goblet cells - mucus
2. Enterocytes - secrete water and electrolytes
Does the small intestine secrete enzymes?
Yes - peptidases and intestinal lipase and enzymes for splitting disaccharides (sucrase, maltase, isomaltase, lactase)
The large intestine is like the small intestine in that it has a lot of these:
However, it does not have:
Crypts of Lieberkuhn. However, it does not have villi, goblet cells, enzymes