GI Physiology (345-349) Flashcards by Tsion Aberra

what cells produce cholecystokinin (located where)

I -cells (in the duodenum and jejunum)

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what four actions does cholecystokinin produce

increased gastric emptying, increased pancreatic secretion, increased gall bladder contraction, increased sphincter of Oddi relaxation

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what triggers release of cholecystokinin

increased fatty acids and amino acids

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via what pathway does CCK act to increase pancreatic secretion

neural muscarinic pathways

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what cells produce gastrin (located where)

G-cells in the antrum of the stomach

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what does gastrin do

increases HCl secretion, increases growth of gastric mucosa, increases gastric motility

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how is gastrin regulated

increased by stomach distension/ alkalinization, amino acids and peptides, vagal stimulation

decreased by pH < 1.5

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which two amino acids are potent stimulators of gastrin secretion

phenylalamine and tryptophan

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which cells produce glucose-dependent insulinotropic peptide (located where)

K cells (duodenum and jejunum)

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what are the functions of glucose-dependent insulinotropic peptide

decreased gastric acid secretion

increased insulin release

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what regulates glucose-dependent insulinotropic peptide secretion

GIP release is stimulated by fatty acids, amino acids and oral glucose

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what’s the other name for glucose-dependent insulinotropic peptide

gastric inhibitory peptide (GIP)

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how does GIP cause more rapid uptake of oral glucose than IV

oral glucose directly stimulates GIP, whereas IV glucose doesn’t –> rapid GIP spike in response to oral glucose load –> rapid insulin secretion

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what produces motilin

small intestines

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what does motilin do

produces migrating motor complexes (MMC’s)

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when is motilin upregulated

during fasting state

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what are motilin receptor agonists used for and name an example of a motilin receptor agonist

motilin receptor agonists are used to sitmulate intestinal peristalsis
(i.e. erythromycin)

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what produces secretin (where are these cells located)

S- cells in the duodenum

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what are the actions of secretin

promote pancreatic bicarb secretion
promote bile secretion
decrease gastrin secretion

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what upregulates secretin

increased acid,

fatty acids in the lumen of the duodenum

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what has to happen in the duodenum before pancreatic enzymes can function

bicarb must neutralize the gastric acid in the lumen

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what cells produce somatostatin (located where)

D-cells in the pancreatic islets and GI mucosa

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what are the actions of somatostatin

decreases secretion of: gastric acid, pepsinogen, pancreatic and small intestine fluid, insulin, and glucagon

decreases gallbladder contraction

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what upregulates somatostatin?

what downregulates somatostatin?

upregulated by acid

downregulated by vagal stimulation

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what does nitric oxide do

increase smooth muscle relaxation (including LES)

what GI regulatory molecule deficiency is thought to underlie achalasia

decreased NO secretion is implicated in increased LES tone of achalasia

what secretes vasoactive intestinal polypeptide (VIP)

parasympathetic ganglia in sphincters, gallblader and small intestines

what are the actions of VIP

increase intestinal water and electrolyte secretion; | increase relaxation of intestinal smooth muscle and sphincters

what upregulates and downregulates VIP

upregulated by distension and vagal stimulation; | decreased by adrenergic input

what is a VIPoma

non-alpha, non-beta islet cell pancreatic tumor that secretes VIP

what are the symptoms of a VIPoma

copious watery diarrhea, hypokalemia and achlorhydria

what is the source and function of intrinsic factor

parietal cells; | binds vitamin B12 and promotes its absorption in the terminal ileum

what is the source and function of gastric acid

produced by parietal cells; | decreases stomach pH

how is gastric acid regulated

upregulated by histamine, ACh, and gastrin | downregulated by somatostatin, GIP, prostaglandin, and somatostatin

where is pepsinogen secreted and what does it do

pepsinogen is secreted by chief cells in the stomach and is cleaved to pepsin by H+ pepsin promotes protein digestion

what upregulates pepsin levels

vagal stimulation and local acid (to activate pepsinogen)

where is bicarb secreted and what does it do

bicarb is secreted in the salivary glands, stomach, duodenum (Brunner's glands) and pancreas; bicarb neutralizes acid

how is bicarb secretion regulated

secretin increases bicarb secretion by promoting pancreatic secretion and biliary secretion

what kinds of secretory cells are found in the body of the stomach

parietal cells and chief cells

what kinds of secretory cells are found in the antrum of the stomach

G cells, mucous cells, D cells (which are found throughout GI mucosa)

what kinds of secretory cells are found in the duodenum

I cells, K cells, S cells, D cells, Brunner's glands

what's the predominant way in which gastrin causes increased HCl secretion

by increasing histamine release from ECL cells

what GPCR type pathway do M3 ACh and CCKb receptors act through

what GPCR type pathway does histamine receptor act through

what GPCR type pathway do prostaglandin and somatostatin receptors act through

what do Brunner's glands secrete and when do they become hypertrophied

alkaline mucus; | they become hypertrophied during peptic ulcer disease

at what flow rate are pancreatic secretions high in bicarb

high flow

at what flow rate are pancreatic secretions high in Cl-

low flow

what is the tonicity of pancreatic secretions

isotonic

what does alpha amylase do? | is it a zymogen?

starch digestion; | not a zymogen (it is secreted in its active form)

name four pancreatic proteases | what form are they secreted in?

trypsin, chymotrypsin, elastase, carboxypeptidase | secreted as zymogens

what enzymes does trypsin cleave/activate

trypsinogen --> trypsin (positive feedback) chymotrypsinogen--->trypsin proelastase --> elastase procarboxypeptidase --> carboxypeptidase

what enzyme cleaves and activates trypsinogen and where does this occur

enterokinase/ enteropeptidase; | found in the duodenal and jejunal mucosa

what size of sugars are taken up by enterocytes (polysaccharides, disaccharides or monosaccharides)

monosaccharides only (glucose, fructose, galactose)

which apical transporters take up glucose and galactose? | which take up fructose?

glucose and galactose are taken up by SGLT1 (Na+ dependent glucose cotransporter) fructose is taken up by facilitated diffusion through GLUT5

how are all sugards transported into the blood

GLUT-2

what does a D-xylose absorption test tell you

D-xylose absorption test tells you if a malabsorption issue is due to damage to the GI mucosa; D-xylose doesn't require any enzymes, just intact mucosa, to be digested so if urine levels are normal there's nothing wrong with the GI mucosa and the problem is some other etiology of malabsorption

where are these absorbed: iron folate B12

iron is absorbed in the duodenum folate is absorbed in the jejunum and ileum B12 is absorbed in the terminal ileum, along with bile acids

describe Peyer's patches and where they are found

unencapsulated lymphoid tissue containing B cells and M cells found in lamina propria and submucosa of ileum

what do the M cells of Peyer's patches do

constantly sample and present antigens to immune cells

when stimulated what do the B cells of Peyer's patches do

form germinal centers and differentiate into IgA-secreting plasma cells

how is IgA transported into the lumen of the gut (what does it gain as it is released into lumen)

intraluminal transport via formation of receptor-IgA complex (exocytosed into lumen with a piece of the complex called secretory component)

what are bile salts made of

bile acids conjugated to glycine or taurine

what are the components of bile

bile salts, phospholipids, cholesterol, bilirubin, water and ions

what catalyzes the rate limiting step of bile synthesis

7 alpha hydroxylase

what are the functions of bile

``` digestion and absorption of lipids and fat-soluble vitamins cholesterol excretion (body's only means of doing so) antimicrobial activity (via membrane disruption) ```