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GI exam 1 > Secretory functions of GI tract peptides ( choudhury) > Flashcards

Secretory functions of GI tract peptides ( choudhury) Flashcards

1
Q

are all GI hormones peptides?

A

yes

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2
Q

how are GI peptides classified ? and what are the three classifications

A

based on method by which peptide is delivered to target site

endocrine
paracrine
neurocrine

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3
Q

what are the 5 GI endocrine hormones

A 
Secretin 
Gastrin
CCK (Cholecystokinin) 
Gastric inhibitory peptide (GIP)
Motilin
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4
Q

where are endocrine peptides released and what do they reach

A

released into circulation and reach all tissues

specific receptors are found on target tissues

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5
Q

what are paracrine peptides released from and where do they diffuse and have effects

A

released from endocrine cells and diffuse through extracellular space to target

have effects in areas where cells are contained which release them

can release or inhibit release of endocrine substances

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6
Q

what is an example of a paracrine substance

A

histamine

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7
Q

what effect does ACH have on the GI tract

A

its not a peptide BUT is a neuroregulator of the GI tract which stimulates acid secretion from gastric parietal cells

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8
Q

what are the three candidate endocrine peptides

A

PP
peptide YY
enteroglucagon

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9
Q

where are endocrine factors released in the GI tract and what are the three stimuli for release

A

released from stomach and small intestine mucosa into portal circulation

after stimulation from nerves, distention, chemical stimulation of food intake

pass through liver and heart back to digestive system to regulate movement, secretions, growth, release of other hormones and absorption

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10
Q

where is the site of release of gastrin

A

G cells in gastric mucosa
duodenum
pancreas

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11
Q

what molecules stimulate the release of gastrin

A

protein
distention due to food
nerves

also:
Ca
Decaffeinated coffee
wine

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12
Q

what inhibits the release gastrin release

A

acid (feedback)

secretin

glucagon

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13
Q

what are the sites of release of CCK

A

duodenum
jejunum
ileum (minor)

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14
Q

what stimulates the release of CCK

A

protein
fat

Acid (of secondary importance)

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15
Q

what part of the GI tract release secretin

A

duodenum

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16
Q

what stimulates the release of secretin

A

acid

fatty acids(of secondary importance)

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17
Q

what part of GI tract releases GIP

A

duodenum

jejunum

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18
Q

what part of GI tract releases Motilin

A

Duodenum

jejunum

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19
Q

what stimulates the release of GIP

A

glucose (primarily)

protein
fat

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20
Q

what stimulates the release of motilin

A

nerves (Main)

of secondary importance:
fat
acid

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21
Q

what is the function of microvilli on the surface of endocrine cells

A

contain receptors that sample luminal contents

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22
Q

what is the major regulatory action of secretin

A

Natures antacid

released when pH falls below 4.5

stimulates pancreatic and liver bicarb and fluid secretion

inhibits gastric emptying (acid secretion)

stimulates pancreatic growth

inhibits gastrin release

23
Q

what is the major regulatory action of gastrin

A

stimulates release of HCl by parietal cells of the stomach via release of histamine from ECL cells and direct action

aids in gastric motility

stimulates GI mucosal growth (can lead to carcinoid tumors)

24
Q

conditions leading to decreased acid release lead to what….

A

high serum gastrin levels

25
Q

what are the major regulatory actions of CCK on the GI tract

A

stimulates gallbladder contractions to release bile for fat digestion and pancreatic bicarb release

stimulates pancreatic growth

inhibits gastric emptying

26
Q

what is the function of GIP

A

inhibits gastric secretions and stimulates insulin release

27
Q

what does motilin do

A

stimulates gastric motility and upper GI motility via the interdigestive migrating myoelectric complex (MMC)

28
Q

what is similar about gastrin and CCK

A

they have 5 identical amino acids on their C terminal

29
Q

what are the two forms of gastrin

A 
G17 (little gastrin)
G 34 (big gastrin)

gastrin is synthesized as a larger precursor molecule called progastrin

30
Q

what form does most gastrin exist in

A

G 34 in the basal or interdigestive state

31
Q

after a meal what is the predominant form of gastrin and what does this cause

A

G17

stimulates gastric secretion

32
Q

because of the similar structure of CCK and gastrin, what can happen.

A

desulfated CCK can activate gastrin receptors responsible for acid secretion (CCK-B receptors)

gastrin can activate CCK receptors responsible for gall bladder contraction (CCK-A receptors)

33
Q

what molecules are similar in structure to secretin

A

Glucagon has 14 AA’s identical to secretin

GIP and VIP have 9 amino acids identical to secretin

34
Q

what is the function of enteroglucagon

A

this is a lesser known candidate endocrine hormone similar to secretin

formed by same gene in pancreatic alpha cells which forms glucagon

releases insulin
inhibits gastric secretion
delays gastric emptying

35
Q

what stimulates the release of enteroglucagon

A

fat

36
Q

what is the function of pancreatic polypeptide

A

“PP”

inhibits pancreatic bicarb and enzyme secretion

37
Q

what stimulates PP release

A

protein, fat, glucose

38
Q

what is the function of peptide YY and what stimulates its release

A

inhibits gastric secretion and emptying as well as intestinal motility

39
Q

what is the function of substance P

A

stimulates intestinal motility

stimulates gallbladder contraction

(neurocrine peptide)

40
Q

what is the function of neurotensin

A

increases blood glucose by stimulation of glycogenolysis and release of glucagon

inhibits release of insulin

41
Q

what is the function of VIP

A

relaxation of smooth muscle (intestine)
vasodilator via promotion of production of NO

stimulates pancreatic secretion
inhibits gastric secretion
stimulates intestinal secretion

(this is a neurocrine peptide)

42
Q

what is the function of Bombesin (aka GRP)

A

released by vagal stimulation with resulting release of gastrin

this is a neurocrine peptide

43
Q

what is the function of enkephalins

what are these used to treat

A

activation of opiate receptors on circular smooth muscle cells to mediate their contraction and also contraction of lower esophageal, pyloric, and ileocelcal sphincters

opiates slow intestinal motility

used to treat diarrhea

44
Q

what is the function of somatostatin (paracrine peptide) and where is it found

A

found in gastric and duodenal mucosa AND pancreas

inhibits gastrin release and gastric acid secretion

45
Q

what is the function of histamine

what cell is histamine produced in

what causes the release of histamine

A

produced in ECL cells

released by gastrin and stimulates acid secretion from parietal cells

potentiates action of gastrin and ACh on acid secretion

46
Q

how do we treat hypersecretion of acid

A

histamine (H2) blockers

47
Q

what is Gastrinoma or Zollinger-Ellison syndrome

A

non-beta cell tumor of the pancreas or duodenal tumors

continually produce and release gastrin into the blood

48
Q

what does gastrinoma result in

A

hypersecretion of gastric acid by parietal cells and increased acid secretory capacity by hyperplastic mucosa

peptic ulcers
diarrhea
steatorrhea (excess fat in feces)
hypokalemia

49
Q

what contributes to the diarrhea that is seen in gastrinoma

A

high gastrin levels inhibit absorption of fluid and electrolytes by the intestine

50
Q

what contributes to the steatorrhea in gastrinoma (fat in the stool)

A

inactivation of pancreatic lipase by gastrin along with precipitation of bile salts at a low luminal pH

51
Q

how is gatrinoma (zollinger-ellison) treated

A

treated with drugs which inhibit acid secretion along with gastrectomy if needed

52
Q

what are the blood tests that indicate gastrinoma

A

elevated serum gastrin

53
Q

what are three tests that can definitively diagnose gastrinoma (considering gastrin is also elevated in duodenal ulcer disease)

A

stimulation by protein meal (no measurable change in serum gastrin levels)

IV Calcium (increased acid and serum gastrin level) 
(ca causes increases gatrin release)
secretin infusion (increased serum gastrin level) 
(secretin typically decreases gastrin levels... but in gastrinoma for unknown reason secretin causes gatrin release)
54
Q

what is the cause of pancreatic cholera (watery diarrhea syndrome)

what does it result in

A

overproduction of VIP due to pancreatic islet cell tumor

results in significant intestinal secretion of fluid and electrolytes with production of lots of diarrhea

frequently lethal due to large volume of fluid and electrolyte loss

GI exam 1 (11 decks)

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