Gastrointestinal Regulatory Substances Flashcards
What substances regulate GI functions?
GI peptides:
hormones
neurocrines
paracrines
What are the release sites of GI peptides?
from endocrine cell or neurons (neurocrine)
What are the routes taken of GI peptides?
travel through blood
OR
act within same tissue
T/F: GI peptides are released from endocrine cells of GIT, not glands.
TRUE
Where do hormones enter?
portal circulation, liver, systemic circulation, target cells
What’s the target(s) of GI hormones?
in GIT or elsewhere
List the 4 GI hormones
gastrin
cholecystokinin (CCK)
secretin
glucose-dependent insulinotropic peptide
Glucose-dependent insulinotropic peptide is also called…
gastric inhibitory peptide (GIP)
Define GI paracrines.
secreted by endocrine cells of GIT
act LOCALLY within SAME tissue
What is the major GI paracrine hormone? What actions does it have?
somatostatin
major inhibitory actions
Define GI neurocrines.
synthesized in neurons of GIT and released after an AP
What are some major neurocrines.
acetylcholine
norepinephrine
gastrin-releasing peptide (GRP)
enkephalins
neuropeptide Y
substance P
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What is the function of gastrin?
promote hydrogen ion secretion (stomach releases HCl)
stimulate growth of gastric mucosa
increase gastric motility
Gastrin is secreted by ______ in the ______
G cells, stomach
What are the two forms of gastrin?
big and little
When is big gastrin secreted?
between meals and low basal levels
When is little gastrin secreted?
in response to a meal —> distention of stomach in presence of AMINO ACIDS and PEPTIDES
Gastrin is a local vagal reflex, where ____ is released from vagal nerves onto G cells.
GRP (gastrin-releasing peptide)
What inhibits gastrin secretion?
low gastric pH
somatostatin (paracrine)
What is Zollinger-Ellison syndrome?
overgrowth of gastrin mucosa
gastronoma (gastrin-secreting tumor)
INCREASES H+ ions
non-beta cell pancreas
What secretes cholecystokinin (CCK)? Where?
I cells of duodenal & jejunal mucosa
CCK is secreted in response to…
presence of fatty acids
amino acids
peptides
What are the 5 actions of CCK?
contraction of gallbladder (emulsify bile)
secretion of pancreatic enzymes (lipases to release FA amylase for starch, proteases for protein)
secretion of HCO3- from pancreas
growth of exocrine pancreas & gallbladder
inhibition of gastric emptying (increases digestion)
Fill in the blanks of CCK actions.
What is secretin secreted by?
S cells of duodenum
What is secretin secreted in response to?
H ions
fatty acids present in small intestine
What does secretin inhibit?
gastrin release from G cells in stomach
Fill in the blanks of secretin actions.
What is gastric-inhibitory peptide (GIP) secreted by?
K cells of duodenum and jejunum
What is GIP secreted in response to?
glucose, amino acids, and fatty acids
What does GIP stimulate?
insulin secretion
What stimulates GIP?
ORAL glucose load
NOT intravenous
What does GIP inhibit?
gastric H ion secretion
gastric emptying and motility
List the candidate hormones.
motilin
pancreatic polypeptide
enteroglucagon
glucagon-like peptide-1 (GLP-1)
What are candidate hormones?
not considered true GI hormones because they fail to meet one or more criteria
- secreted by GIT
What is motilin secreted by?
upper duodenum during FASTING
What does motilin stimulate?
GI motility
interdigestive myoelectric complexes at 90 minute intervals
- trigger peristaltic waves
What is pancreatic polypeptide secreted by?
pancreas in response to ingestion of carbs, proteins, and lipids
What does pancreatic polypeptide do?
self-regulates pancreatic secretion
inhibits pancreatic secretion of HCO3- and enzymes
What is enteroglucagon secreted by?
intestinal cells in response to decreased blood glucose
What does enteroglucagon stimulate?
stimulate liver to increase glyconolysis and gluconeogenesis
What does glucagon-like peptide-1 (GLP-1) stimulate?
insulin secretion from pancreatic beta cells
Glucagon-like peptide-1 (GLP-1) is secreted by?
L cells of small intestine
What is secreted in response to nutrient indigestion?
glucagon-like peptide-1 (GLP-1)
What does glucagon-like peptide-1 inhibit?
inhibits glucagon secretion
inhibits gastric emptying
inhibits appetite
What is somatostatin secreted by? In response to what?
D cells of GI mucosa
in response to decreased luminal pH
What does somatostatin inhibit?
secretion of other GI hormones
gastric H ion secretion
Where is major secretion of histamine?
H-ion secretion area of stomach
What does histamine stimulate?
H ion secretion by gastric parietal cells
Histamine is a _________.
paracrine
Where are neurocrines synthesized?
cell bodies of GI neurons
An ________ causes a release of a neurocrine.
action potential
Where is a release point for neuromodulators? (peptidergic)
postganglionic non-cholinergic parasympathetic neurons
- VIP
- substance P
- GRP
- enkephalins
- neuropeptide Y
Where is the satiety center located?
ventromedial nucleus (VPN) of hypothalamus
- something to do with arcuate nucleus
What does the satiety center do?
inhibit appetite even in presence of food
_________ neurons release pro-opiomelanocortin (POMC)
anorexigenic
- satiety center
Where is the feeding center located?
lateral hypothalamic area (LHA)
- something to do with arcuate nucleus
_______ neurons release neuropeptide Y
orexigenic
- feeding center
Fill in the blanks.
