GI Hormones
Satiety hormones:
CCK, glucagon like peptide 1, peptide YY
What is the source of somatostatin?
D cells in stomach and duodenum, delta cells of pancreatic islets
Where is somatostatin released?
D cells of stomach and duodenum, delta cells of pancreatic islets
Where is glucagon like peptide 1 released from?
EEC cells in the gut wall
What is the source of VIP?
ENS neurons
What is the target for gastrin releasing peptide?
G cells in antrum of stomach
What cell secretes CCK?
I cells
Where is cholecystokinin released from?
I cells in duodenum and jejunum neurons in ileum and colon
What is the source of GIP?
K cells in duodenum and jejunum
Where is gastric inhibitory peptide released from?
K cells in duodenum and jejunum
Where is secretin released from?
S cells in small intestine
What stimulates relaxation on caudal side during peristalsis?
VIP and NO
What stimulates contraction on orad side during peristalsis?
acetylcholine, substance P
Starch digesting enzyme:
amylase
What is glucagon like peptide 1 involved in regulating?
blood glucose levels via insulin secretion stimulation reduction of appetite and food intake delays in gastric emptying
What is the purpose of peptide YY in the pancreas?
decrease enzyme and fluid secretion
What is the action of secretin on the stomach?
decrease gastric acid secretion
What is the action of peptide YY in the stomach?
decrease vagally mediated acid secretion
What are the actions of gastrin inhibitory peptide?
decreased fluid absorption (exocrine) increased insulin release (endocrine)
Nucleases:
deoxyribonuclease and ribonuclease
What types of stimuli regulate timing of secretions from dueodenum?
distension, presence of protons in chyme, high osmolarity of chyme (due to increased glucose, I think), presence of various macromolecules in lumen
What is the action of gastrin releasing peptide?
don't overthink this - its to increase gastrin release
What is the source of neurotensin?
endocrine cells in ileum
What is the source of peptide YY?
endocrine cells in ileum and colon
Where is peptide YY released from?
endocrine cells in ileum and colon
Where is motilin released from?
endocrine cells in upper GI tract
What type of peptidase is chymotrypsinogen, and what are its products?
endopeptidase, oligopeptides
What type of peptidase is proelastase, and what are its products?
endopeptidase, oligopeptides
What type of peptidase is trypsin, and what are its products?
endopeptidase, oligopeptides
What type of peptidase is typsinogen, and what are its products?
endopeptidase, oligopeptides
What releases 5HT in the colon?
enterochromaffin cells
What are the targets of motilin?
esophageal sphincter, stomach, and duodenum
What type of peptidase is procarboxypeptidase A and B, and what are its products?
exopeptidases, single amino acids (A-neutral, B-basic)
Bile performs what fuctions:
forms micelles to shield hydrophobic aspects of lipid digestion to make them more soluble bile acids act as detergents
Chief cells release large quantities of _________ __________ which adsorbs to the surface of _________ ___________.
gastric lipase, lipid droplets
What does activation of intrinsic neurons in the gastric phase lead to?
gastrin releasing peptide - which leads to release of gastrin from G cells
Where is guanylin released from?
ileum and colon
What is the action of secretin in the pancreas?
increase HCO3 and fluid secretion by pancreatic ducts
What is the action of motilin?
increase smooth muscle contraction (increase GI motility)
What is the action of guanylin?
increased fluid absorption
Lipid digesting enzymes or precursors:
lipase, nonspecific esterase, prophospholipase A2
What cell releases secretin and with what stimulus?
low duodenal pH stimulates release from S cells
What is responsible for phase 3 contractions (between meals) with the migrating motor complex?
motilin
What gland increases acid and pepsin?
oxyntic gland
What is the target organ for gastric inhibitory peptide?
pancreas
What are the target organs for cholecystokinin?
pancreas and gallbladder
What are the targets of secretin?
pancreas and stomach
What are the three lipases found in duodenal pancreatic juice?
pancreatic lipase, phospholipase A2, cholesterol esterase
What are the five very general products of pancreatic acinar cells?
precursors of proteases, starch digesting enzymes, lipid digesting enzymes and precursors, nucleases, regulatory factors
What is glucagon like peptide 1 secreted in response to?
presence of luminal carbohydrates and lipids
Regulatory factors:
procolipase, trypsin inhibitors, monitor peptide
Macronutrients in chyme, when delivered to duodenum, lead to what?
release of pancreatic and biliary secretions, and the activation of hormonal, paracrine, and neural pathways regulating gastric emptying
What is CCK(B) receptors sensitive to, and where are they found?
responsive to gastrin and CCK, and found on parietal cells
What hormone triggers release of bicarb from pancreas?
secretin
What three factors mediate the pressure gradient from the stomach to the duodenum?
serotonin, NO, NE
What duodenal feedback is elicited when chyme enters?
slowed gastric emptying (vagal), CCK released, gallbladder contraction (CCK), pancreatic secretion, relaxation of sphincter of Oddi (CCK)
What are the targets of guanylin?
small and large intestine
Secretions into the GI tract are regulated by the opening and closing of:
sphincter of Oddi
What are the actions of cholecystokinin?
stimulate enzyme secretion and contraction
Peptide YY stimulation and actions:
stimulated by presence of lipids in lumen, leads to inhibition of Cl- burst and thus fluid secretion -> slows propulsion to allow more time for digestion and absorption in ileum
What is the chain of events once secretin is released?
stimulates secretion of bicarb from pancreatic epithelial cell, water follows, opens up CFTR and causes outflow of Cl- to drive antiporter of bicarb
What is the target of somatostatin?
stomach
What are the targets of peptide YY?
stomach and pancreas
Action of CCK:
travels in bloodstream to CCKA receptors, stimulates neural reflex pathways, release of GRP and VIP, causes rise in intracellular Ca2+ leading to vesicle fusion and release of acinar enzymes into duct also stimulates gallbladder contraction -> release of bile causes relaxion of sphincter of Oddi
What are the precursors of proteases?
trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase A and B
Where is gastrin releasing peptide released from?
vagal nerve endings
What two hormones relax the internal anal sphincter?
vasoactive intestinal polypeptide (VIP) and NO
