Transcript Slide 1
Regulation of GIT
• Hormones
• Paracrine
•
Neurocrines
GI Hormones
• Secretin
• Gastrin
• Cholecystokinin (CCK)
• Gastric Inhibitory Peptide (GIP)
• Motilin
Gastrin - Chemistry
• Molecular forms - G-17, G-34, G-14
Gastrin - Distribution and Release
• Release
- Released from G cells in antrum and duodenum
- Stimuli - protein digestion products
- nervous, physical distention
- (calcium, coffee,and wine)
- Inhibition
- acidification of antrum
• Response to meal - Large amounts of G-17 released from antrum
- Small amounts of G-34 released from duodenum
Gastrin - Physiological Effects
• Gastric acid secretion
- 1,500x more potent than histamine
• Trophic activity
- Stimulates growth of oxyntic mucosa of stomach,
duodenal mucosa, and colon mucosa
- Surgical removal of antrum causes atrophy
- Patients with gastrin secreting tumors have
mucosal hyperplasia and hypertrophy
Gastrinoma - Zollinger-Ellison syndrome
• Gastrin secreting tumor
- Non-beta cell tumor of pancreas (80%) or G-cell
tumors in duodenum (10-15%)
- Continually secretes gastrin into blood
• Symptoms
- Duodenal ulcers, diarrhea, steatorrhea,
hypokalemia
• Hypergastrinemia causes hypersecretion
of acid
- Increased parietal cell mass
- Constant stimulation of hyperplastic mucosa
Cholecystokinin - Chemistry
• Molecular form - 8-AA, 33-AA, 39-AA, 58-AA
CCK - Distribution and Release
• Released from I-cells in duodenum and
jejunum
• Stimuli for release
- Fatty acids or monoglycerides (not triglycerides)
- peptides and amino acids
- Acid (weak)
CCK - Physiological Effects
• Emptying of gallbladder - contracts gallbladder, relaxes sphincter of Oddi
• Pancreatic exocrine
- Potent stimulator of enzyme secretion
- Weak stimulator of bicarbonate secretion (but can
potentiate secretin effects)
• Inhibits gastric emptying
• Trophic effects - exocrine pancreas and
gallbladder mucosa
Secretin - Chemistry
• Molecular form - 27-AA peptide
Secretin
• Released from S-cells of duodenal mucosa
• Stimuli for release
- Acid in duodenum (pH <4.5)
- Fatty acids in duodenum
• Physiological effects - “Nature’s Antiacid”
-
Inhibits gastric acid secretion
Stimulates pancreatic and bile bicarbonate secretion
Stimulates pepsin secretion
Trophic effect on exocrine pancreas
Gastric Inhibitory Peptide (GIP)
• Chemistry - Member of secretin family
- 9 AA identical to secretin in kind and position
• Stimuli / release - Released from duodenum and proximal jejunum
- All major foodstuffs
• Physiological effects - Stimulates insulin release (also called glucosedependent insulinotrophic peptide - GIP)
- Inhibits gastric acid secretion
Motilin
• Chemistry - 22 AA peptide
• Stimuli / release - Released from duodenum and proximal jejunum during
fasting at 100 min intervals
- Release is under neural control
• Physiological effects - Stimulates upper G.I. motility
- Accounts for the migrating motility complex,
“housekeeping contractions”
Neurocrines
Peptide
VIP
GRP
(Bombesin)
Enkephalins
Location
Gut mucosa and
SM
Gastric mucosa
Gut mucosa and
SM
Action
Relaxation of gut
SM
Gastrin Release
SM tone
VIP, vasoactive intestinal peptide, GRP, gastrin-releasing peptide