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Bio& 242 Unit 1 / Lecture 4. Hormonal control in the Digestive system: Gastric hormones. GASTRIN : Secretion: By enteroendocrine (G) cells in gastric pits of the mucosa. Stimulus: Stomach distention and acid pH of chyme causes Gastrin. Action: 1. increases HCl production in stomach
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Hormonal control in the Digestive system: Gastric hormones GASTRIN: Secretion: By enteroendocrine (G) cells in gastric pits of the mucosa. Stimulus: Stomach distention and acid pH of chyme causes Gastrin. Action: • 1. increases HCl production in stomach • 2. increases gastric motility • 3. stimulates growth of gastric mucosa • 4. contract lower esophageal sphincter • 5. relaxes pyloric sphincter • 6. relaxes ileocecal sphincter
Hormonal control in the Digestive system: Gastric hormones Somatostatin: Secretion: By enteroendocrine (D) cells in gastric pits of the mucosa in the pylorus. Stimulus: continuously released, overridden by Gastrin and nerves Action: • Inhibition of Gastrin production
Hormonal control in the Digestive system: Small Intestinal hormones SECRETIN: Secretion: By Enteroendocrine (S) cells in the Crypts of Lieberkuhn of small intestine. Stimulus: Acid chyme in small intestine causes secretion of Secretin: Actions: • stimulate secretion of pancreatic juice and bile that is rich in bicarbonate ions. • inhibit production of HCl in stomach • promote growth and maintenance of the pancreas • enhance effects of Cholecystokinin (CCK) • Increases rate of bile secretion by hepatocytes
Hormonal control in the Digestive system: small intestinal hormones CHOLECYSTOKININ (CCK): Secretion: Enteroendocrine (CCK) cells in the small intestine mucosa Crypts of Lieberkuhn Stimulus: Chyme rich in amino acids, triglycerides and fatty acids enter the small intestine. Actions: • increases secretion of pancreatic juice rich in digestive enzymes • opens the Sphincter of Oddi • contracts the gallbladder • Inhibits gastric secretion and motility • May reduce hunger
Hormonal control in the Digestive system: small intestinal hormones Gastric Inhibitory Peptide (GIP): Secretion: Enteroendocrine cells in the small intestine mucosa Crypts of Lieberkuhn Stimulus: Chyme rich in triglycerides, fatty acids, and glucose enter the small intestine. Actions: • Stimulates release of insulin by beta cells • Inhibits gastric secretion and motility • Stimulates lipogenesis by adipose tissue • Stimulates glucose use by skeletal muscle cells
Hormonal control in the Digestive system: small intestinal hormones Vasoactive Intestinal Peptide (VIP): Secretion: Enteroendocrine cells in the small intestine mucosa Crypts of Lieberkuhn Stimulus: Chyme entering the small intestine. Actions: • Stimulates buffer secretion • Inhibits gastric secretion • Dilates intestinal capillaries
Hormonal control in the Digestive system Pancreas and Islets of Langerhans Endocrine cells make up 1% of the pancreas and are observed as Islets of Langerhans: 1. Alpha Cells: Secrete Glucagon (increases blood sugar) 2. Beta Cells: Secrete Insulin (decreases blood sugar) 3. Delta Cells: Secretes Somatostatin (inhibits secretion of both glucagon and insulin and prolongs rate of nutrient absorption / decrease depletion) 4. F-Cells: Secrete Pancreatic Polypeptide (inhibit secretion of digestive enzymes and inhibits contraction of the gallbladder)