1. General Intestinal Histology

2. Activities of the Gastrointestinal Tract u Motility u Secretion u Digestion u Absorption

3. Intestinal Autonomic Nervous System

4. Parasympathetic Nervous System

5. Vagovagal or Long reflex

6. The Enteric Nervous System

7. Peptide Secretion

8. Criteria for GI Hormones u a physiologic stimulus in one part of the GI tract produces a response in another part u the response must be independent of the nervous system u the physiologic response can be duplicated with an “extract” from the stimulus site u the substance must be isolated, purified, identified chemically, and synthesized

9. Gastrin u Stimulates gastric acid secretion and growth of gastric oxyntic gland mucosa. u Released from the gastric antrum and perhaps the duodenum. u Release is stimulated by peptides, amino acids, gastric distention and stimulation of the vagus.

10. Structure of Human “little” Gastrin

11. Cholecystokinin (CCK) u Stimulates gallbladder contraction, pancreatic enzyme and bicarbonate secretion, and growth of the exocrine pancreas u Inhibits gastric emptying u Released from the duodenum and jejunum u Release is stimulated by peptides, amino acids and >8C fatty acids, and to a lesser extent by acid

12. Structure of porcine Cholecystokinin

13. Secretin u Stimulates pancreatic bicarbonate secretion, biliary bicarbonate secretion, growth of the exocrine pancreas, and pepsin secretion u Inhibits gastric acid secretion and the trophic effect of gastrin u Secreted by the duodenum u Secretion is stimulated by acid and to a lesser extent fat

14. Secretin Family of Peptides

15. Gastric Inhibitory Peptide (GIP) u Stimulates insulin release u Inhibits gastric acid secretion u Secreted by the duodenum and jejunum u Secretion is induced by glucose, amino acids and fatty acids

16. Motilin u Stimulates gastric and intestinal motility u Released by the duodenum and jejunum u Release is stimulated by nerves, fat and acid

17. Candidate Hormones u Pancreatic polypeptide-a 36 amino acid peptide released from the pancreas in response to all three food stuffs u Peptide YY-a 36 amino acid peptide released from the ileum and colon in response to meals, especially fat u Enteroglucagon-is present in the distal small intestine and released into the bloodstream

18. Paracrines u Act on cells in the immediate vicinity, not through the blood stream. –Somatostatin –Histamine

19. Somatostain u Inhibits gastrin release, release of other peptide hormones and gastric acid secretion. u Released from the GI mucosa and the pancreatic islets. u Release is induced by acid. u Release is inhibited by vagal stimulation.

20. Histamine u Stimulates gastric acid secretion. u Released from oxyntic gland mucosa and enterochromaffin-like (ECL) cells. u Released in response to gastrin.

21. Neurocrines u Released from neurons by an action potential, then diffuse across the synaptic cleft to the target tissue –Vasoactive intestinal peptide (VIP) –Bombesin or gastrin-releasing peptide (GRP) –Enkephalins

22. Vasoactive Intestinal Peptide u Stimulates intestinal and pancreatic secretion. u Relaxes sphincters and gut circular smooth muscle in general. u Released by cells in the mucosa and smooth muscle of the GI tract.

23. Bombesin or Gastrin-releasing peptide u Stimulates gastrin release. u Released by cells in the gastric mucosa.

24. Enkephalins u Stimulates smooth muscle contraction. u Inhibits intestinal secretion. u Released from cells in the GI mucosa and smooth muscle.

25. Smooth Muscle Cells u They are smaller than skeletal muscle cells and long, narrow and spindle-shaped. u Cells that belong to a bundle are functionally coupled by gap junctions. u There are no sacromeres, therefore no striations. u The ratio of thin to thick filaments is 15:1.

26. u Robert D. Specian, Ph.D. u rspeci@lsuhsc.edu