1. HORMONES OF THE GASTROINTESTINAL TRACT

2. Dr. M. Alzaharna (2014) Gastric and Intestinal Glands The gastric and intestinal glands are embedded in the mucosa They are comprised of single layers of epithelial cells arranged to form deep invaginations of the mucosal surface called pits in the stomach and crypts in the intestines Cells that secrete hormones are called enteroendocrine cells

3. Dr. M. Alzaharna (2014) Gastrin Produced from G cells in the antrum of the stomach and to a lesser extent in the proximal portion of the duodenum Release is increased by stomach distension, peptides, amino acids, caffeine, parasympathetic innervation Release is inhibited by highly acidic pH (< 2.0) Functions include: – Increases gastric secretions (primarily HCl) – Increases histamine release; – Increases gastric motility; – stimulates growth of gastric mucosa

4. Stimulation Of Gastric Acid Secretion Enterochromaffin-like (ECL) cells Neurotransmitter PACAP (pituitary adenyl cyclase activating peptide) GRP (gastrin releasing peptide)

5. Dr. M. Alzaharna (2014) Somatostatin Produced by D cells of the stomach – Secretion is stimulated by activation of the sympathetic nervous system and by acidic pH, – and is inhibited by activation of the parasympathetic nervous system, continuously released, overridden by gastrin and nerves Functions include: – Inhibit gastrin and histamine secretion – also directly inhibits acid release from parietal cells

6. Dr. M. Alzaharna (2014) Secretin Secretin is produced in S cells in the duodenal and proximal jejunal mucosa Secretion is stimulated by arrival of acidic chyme in duodenum Functions include : – Stimulates bicarbonate secretion from pancreas – Inhibits gastric secretion by inhibiting gastrin release – Decreases gastric motility – Increases hepatic bile production, increases CCK – Promotes growth and maintenance of the pancreas

7. Dr. M. Alzaharna (2014) Cholecystokinin (CCK) Produced by I cells in the duodenal and jejunal mucosa Release is stimulated by fatty acids in duodenum (also amino acids, acidic chyme) Functions: – Causes gallbladder contraction – Stimulates release of pancreatic enzymes – Decreases gastric motility and secretion (increases somatostatin release)

8. Dr. M. Alzaharna (2014) Gastric Inhibitory Peptide (GIP) GIP is synthesized and secreted by K cells, which reside mainly in the proximal duodenum and to a lesser extent in the jejunum Release is stimulated in response to Chyme rich in triglycerides, fatty acids, and glucose in the small intestine Functions: – Stimulates release of insulin by beta cells – Inhibits gastric secretion and motility – Stimulates lipogenesis by adipose tissue – Stimulates glucose use by skeletal muscle cells

9. Dr. M. Alzaharna (2014) Vasoactive Intestinal Peptide (VIP) VIP is synthesized and secreted in Enteroendocrine cells in the small intestine mucosa Release is stimulated in response to Chyme entering the small intestine Functions: – Stimulates buffer secretion – Inhibits gastric secretion – Dilates intestinal capillaries