gastrointestinal hormomes & their role in secretomotor fuction of the gut
TRANSCRIPT
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GI HORMONES & THEIR ROLE
IN SECRETOMOTOR
FUNCTION OF THE GUT
RK Goit, Lecturer
Department of Physiology
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GI Hormones - secreted from the endocrine cells
especially in stomach & small intestine
endocrine cells
Enteroendocrine - GI hormones
Enterochromaffin - serotonin
APUD – amines & polypeptides (neuroendocrine cells)
Carcinoid tumors originate from neuroendocrine
cells.
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1. Gastrin family-gastrin & CCK
2. Secretin family-secretin, glucagon, GLI, VIP &
GIP
3. Other polypeptides
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Gastrin
pyloric glands (G Cells)-antral portion of the
stomach
also found in the pancreatic islets in fetal life
anterior & intermediate lobes of the pituitary
gland, in the hypothalamus, medulla oblongata, &
in the vagus & sciatic nerves
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a polypeptide hormone
heterogeneity
Macroheterogeneity-peptide chains of various length
Microheterogeneity-differences in molecular structure
G 34, G 17, G 14 (depending on number of AA)
G 17- principal gastrin secreted from the stomach
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Functions
stimulation of gastric acid & pepsin secretion
stimulates growth of gastric mucosa & mucosa of
intestine
↑ gastric motility
contraction of muscles at the gastro-esophageal
junction
exocrine pancreatic secretion
insulin secretion
stimulates mass movement of large intestine
colonic contraction that initiates gastrocolic reflex
after a meal
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Stimulate that ↑ gastrin secretion
Luminal
Peptides & amino acids
Distension
Neural
↑ vagal discharge via GRP
Blood-borne
Calcium
Epinephrine
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Stimulate that ↓ gastrin secretion
Luminal
Acid
Somatostatin
Blood-borne
Secretin, GIP, VIP, Glucagon
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Cholecystokinin-Pancreozymin
(CCK-PZ or CCK)
I cells in the upper intestine
nerves in the distal ileum & colon
neurons in brain ( cerebral cortex) & in nerves in
many part of the body
peptides & amino acids, & long chain fatty acids
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polypeptide hormone
heterogeneity
CCK 58, CCK 39, CCK 33, CCK 12, CCK 8, CCK 4
Duodenum & jejunum CCK 12, CCK 8
Enteric & pancreatic nerves CCK 4
Brain CCK 58, CCK 8
half-life of CCK is about 5 minutes
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Functions
pancreatic secretion rich in enzymes
augments the action of secretin to produce alkaline pancreatic secretion
relaxation of sphincter of Oddi
stimulate growth of pancreas
inhibits gastric acid secretion
inhibits gastric motility-delays gastric emptying
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causes contraction of gall bladder
↑ secretion of enterokinase
enhance motility of small intestine
stimulates colonic movements
augments contraction of pyloric sphincter
stimulates glucagon secretion
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Secretin
S cells located in the mucosa of the upper part of
small intestine (duodenum & jejunum)
polypeptide hormone (27 AA)
acid chyme (↓ 4.5-5.0)- secretin
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Functions
↑ secretion of pancreatic juice rich in bicarbonate
↑ alkaline bile secretion
augments the action of CCK to produce pancreatic
secretion rich in enzymes
↓ gastric acid secretion & motility
contraction of pyloric sphincter
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Glucagon & Glicentin
Preproglucagon (179 AA)
A cells L cells
pancreatic islets lower GIT
upper GIT
Glucagon Glicentin
produces hyperglycemia
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VIP
polypeptide containing 28 AA
nerves in the GIT
also found in blood
also found in the brain & autonomic nerves
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Functions
↑ intestinal secretion rich in electrolytes & water
causes vasodilation
↓ GI motility
potentiates the action of acetylcholine on salivary
glands
inhibits gastric acid secretion
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GIP
polypeptide hormone containing 42 AA
K cells present in the mucosa of duodenum &
jejunum
inhibits gastric acid secretion & motility
stimulate insulin secretion
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Motilin
polypeptide hormone containing 22 AA
enterochromaffin cells & Mo cells present in the
mucosa of GIT
↑ GI motility (interdigestive phase)
a major regulator of MMC
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Neurotensin
a polypeptide hormone containing 13 AA
neurons & mucosal cells of ileum
inhibits gastric acid secretion but ↑ ileal blood
flow
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Substance P
Endocrine & nerve cells in the GIT
↑ intestinal motility of the small intestine
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Somatostatin
a polypeptide containing either SS 14 or SS 28
D cells in GIT, hypothalamus, D cells of pancreas
inhibits secretion of gastrin, VIP, GIP, secretin &
motilin
inhibits pancreatic exocrine secretion; gastric acid
secretion & motility; gall bladder contraction; &
absorption of glucose, amino acids & triglycerides
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GRP
polypeptide containing 27 AA
vagal nerve endings that terminate on G cells
↑ gastrin secretion
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Guanylin
polypeptide hormone containing 15 AA
secreted form the paneth cells
↑ secretion of Cl- into the intestinal lumen
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Peptide YY
entire GIT (ileum & colon)
inhibits the food intake
inhibits gastric acid secretion & motility
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Ghrelin
polypeptide (28 AA)
oxyntic cells of stomach (intestine)
↓ when food is eaten & ↑ during fasting
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References
Ganong Review of Medical Physiology, 22/E
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