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24.13 Three Phases of Gastric Secretion Slide number 1 Cephalic Phase 1. The taste or smell of food, tactile sensations of food in the mouth, or even thoughts of food stimulate the medulla oblongata (green arrow). Taste or smell of food Tactile sensation in mouth 2. Parasympathetic action potentials are carried by the vagus nerves to the stomach (pink arrow). 3. Preganglionic parasympathetic Medulla oblongata 1 vagus nerve fibers stimulate postganglionic neurons in the enteric plexus of the stomach. 5 Vagus nerves 4. Postganglionic neurons stimulate secretion by parietal and chief cells and stimulate gastrin secretion by endocrine cells. 2 3 Gastrin 4 Circulation 5. Gastrin is carried through the circulation back to the stomach (purple arrow), where it stimulates secretion by parietal and chief cells. Secretions stimulated Stomach Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Cephalic Phase Slide number 2 Taste or smell of food Tactile sensation in mouth Medulla oblongata The taste or smell of food, tactile sensations of food in the mouth, or even thoughts of food stimulate the medulla oblongata (green arrow). Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Cephalic Phase Slide number 3 Vagus nerves Parasympathetic action potentials are carried by the vagus nerves to the stomach (pink arrow). Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Cephalic Phase Slide number 4 Vagus nerves Preganglionic parasympathetic vagus nerve fibers stimulate postganglionic neurons in the enteric plexus of the stomach. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Cephalic Phase Slide number 5 Gastrin Stomach Postganglionic neurons stimulate secretion by parietal and chief cells and stimulate gastrin secretion by endocrine cells. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Cephalic Phase Slide number 6 Secretions stimulated Gastrin Circulation Gastrin is carried through the circulation back to the stomach (purple arrow), where it stimulates secretion by parietal and chief cells. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Slide number 7 Vagus nerves Medulla oblongata 1 Gastric Phase Secretions stimulated 1. Distention of the stomach activates a parasympathetic reflex. Action potentials are carried by the vagus nerves to the medulla oblongata (green arrow). 2 Distention 2. The medulla oblongata stimulates stomach 3 secretions (pink arrow). 3. Distention of the stomach also activates local reflexes that increase stomach secretions (purple arrow). Stomach Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Local reflexes stimulated by stomach distention 24.13 Three Phases of Gastric Secretion Gastric Phase Slide number 8 Vagus nerves Medulla oblongata Distention Stomach Local reflexes stimulated by stomach distention Distention of the stomach activates a parasympathetic reflex. Action potentials are carried by the vagus nerves to the medulla oblongata (green arrow). Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Gastric Phase Slide number 9 Vagus nerves Secretions stimulated Decreased gastric secretions Stomach The medulla oblongata stimulates stomach secretions (pink arrow). Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Gastric Phase Slide number 10 Distention Stomach Local reflexes stimulated by stomach distention Distention of the stomach also activates local reflexes that increase stomach secretions (purple arrow). Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Slide number 11 Intestinal Phase 1. Chyme in the duodenum with Vagus nerves a pH less than 2 or containing fat digestion products (lipids) inhibits gastric secretions by three mechanisms. Medulla oblongata 2. Sensory vagal action potentials Vagus to the medulla oblongata nerves (green arrow) inhibit motor action potentials from the medulla oblongata (pink arrow). Decreased gastric secretions 2 Local reflexes 1 3. Local reflexes inhibit gastric pH<2 or lipids 3 secretion (orange arrows). 4. Secretin, gastric inhibitory polypeptide, and cholecystokinin produced by the duodenum (brown arrows) inhibit gastric secretions in the stomach. Secretin, gastric inhibitory peptide, cholecystokinin 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Circulation 24.13 Three Phases of Gastric Secretion Intestinal Phase Slide number 12 pH<2 or lipids Chyme in the duodenum with a pH less than 2 or containing fat digestion products (lipids) inhibits gastric secretions by three mechanisms. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Intestinal Phase Slide number 13 Mechanism One Medulla oblongata Vagus nerves Decreased gastric secretions Vagus nerves pH<2 or lipids Sensory vagal action potentials to the medulla oblongata (green arrow) inhibit motor action potentials from the medulla oblongata (pink arrow). Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Intestinal Phase Slide number 14 Mechanism Two Decreased gastric secretions pH<2 or lipids Local reflexes Local reflexes inhibit gastric secretion (orange arrows). Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.13 Three Phases of Gastric Secretion Intestinal Phase Slide number 15 Mechanism Three Decreased gastric secretions pH<2 or lipids Circulation Secretin, gastric inhibitory peptide, cholecystokinin Secretin, gastric inhibitory polypeptide, and cholecystokinin produced by the duodenum (brown arrows) inhibit gastric secretions in the stomach. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.