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Regulation of GIT

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

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Regulation of GIT

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  1. Regulation of GIT • Hormones • Paracrine • Neurocrines

  2. GI Hormones • Secretin • Gastrin • Cholecystokinin (CCK) • Gastric Inhibitory Peptide (GIP) • Motilin

  3. Gastrin - Chemistry • Molecular forms - G-17, G-34, G-14

  4. 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

  5. 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

  6. 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

  7. Cholecystokinin - Chemistry • Molecular form - 8-AA, 33-AA, 39-AA, 58-AA

  8. 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)

  9. 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

  10. Secretin - Chemistry • Molecular form - 27-AA peptide

  11. 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

  12. 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 glucose-dependent insulinotrophic peptide - GIP) • Inhibits gastric acid secretion

  13. 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”

  14. Neurocrines Peptide Location Action VIP GRP (Bombesin) Enkephalins Gut mucosa and SM Gastric mucosa Gut mucosa and SM Relaxation of gut SM  Gastrin Release  SM tone VIP, vasoactive intestinal peptide, GRP, gastrin-releasing peptide

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