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General Intestinal Histology

General Intestinal Histology. Activities of the Gastrointestinal Tract. Motility Secretion Digestion Absorption. Intestinal Autonomic Nervous System. Parasympathetic Nervous System. Vagovagal or Long reflex. The Enteric Nervous System. Peptide Secretion. Criteria for GI Hormones.

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General Intestinal Histology

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  1. General Intestinal Histology

  2. Activities of the Gastrointestinal Tract • Motility • Secretion • Digestion • 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 • a physiologic stimulus in one part of the GI tract produces a response in another part • the response must be independent of the nervous system • the physiologic response can be duplicated with an “extract” from the stimulus site • the substance must be isolated, purified, identified chemically, and synthesized

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

  10. Structure of Human “little” Gastrin

  11. Cholecystokinin (CCK) • Stimulates gallbladder contraction, pancreatic enzyme and bicarbonate secretion, and growth of the exocrine pancreas • Inhibits gastric emptying • Released from the duodenum and jejunum • 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 • Stimulates pancreatic bicarbonate secretion, biliary bicarbonate secretion, growth of the exocrine pancreas, and pepsin secretion • Inhibits gastric acid secretion and the trophic effect of gastrin • Secreted by the duodenum • Secretion is stimulated by acid and to a lesser extent fat

  14. Secretin Family of Peptides

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

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

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

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

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

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

  21. Neurocrines • 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 • Stimulates intestinal and pancreatic secretion. • Relaxes sphincters and gut circular smooth muscle in general. • Released by cells in the mucosa and smooth muscle of the GI tract.

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

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

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

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

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