1. 24.13 Three Phases of Gastric Secretion Slide number 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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). 2. Parasympathetic action potentials are carried by the vagus nerves to the stomach (pink arrow). 3. Preganglionic parasympathetic vagus nerve fibers stimulate postganglionic neurons in the enteric plexus of the stomach. 4. Postganglionic neurons stimulate secretion by parietal and chief cells and stimulate gastrin secretion by endocrine cells. 5. Gastrin is carried through the circulation back to the stomach (purple arrow), where it stimulates secretion by parietal and chief cells. Cephalic Phase Gastrin Circulation Secretions stimulated Taste or smell of food Tactile sensation in mouth Medulla oblongata Vagus nerves Stomach 1 2 3 5 4

2. 24.13 Three Phases of Gastric Secretion Slide number 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Medulla oblongata Cephalic Phase

3. 24.13 Three Phases of Gastric Secretion Slide number 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parasympathetic action potentials are carried by the vagus nerves to the stomach (pink arrow). Vagus nerves Cephalic Phase

4. 24.13 Three Phases of Gastric Secretion Slide number 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Preganglionic parasympathetic vagus nerve fibers stimulate postganglionic neurons in the enteric plexus of the stomach. Vagus nerves Cephalic Phase

5. 24.13 Three Phases of Gastric Secretion Slide number 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cephalic Phase Postganglionic neurons stimulate secretion by parietal and chief cells and stimulate gastrin secretion by endocrine cells. Gastrin Stomach

6. 24.13 Three Phases of Gastric Secretion Slide number 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cephalic Phase Gastrin is carried through the circulation back to the stomach (purple arrow), where it stimulates secretion by parietal and chief cells. Gastrin Circulation Secretions stimulated

7. 24.13 Three Phases of Gastric Secretion Slide number 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stomach Local reflexes stimulated by stomach distention Distention Secretions stimulated Vagus nerves Medulla oblongata 1. Distention of the stomach activates a parasympathetic reflex. Action potentials are carried by the vagus nerves to the medulla oblongata (green arrow). 2. The medulla oblongata stimulates stomach secretions (pink arrow). 3. Distention of the stomach also activates local reflexes that increase stomach secretions (purple arrow). Gastric Phase 1 2 3

8. 24.13 Three Phases of Gastric Secretion Slide number 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Local reflexes stimulated by stomach distention Distention Vagus nerves Medulla oblongata Distention of the stomach activates a parasympathetic reflex. Action potentials are carried by the vagus nerves to the medulla oblongata (green arrow). Gastric Phase Stomach

9. 24.13 Three Phases of Gastric Secretion Slide number 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gastric Phase Secretions stimulated The medulla oblongata stimulates stomach secretions (pink arrow). Vagus nerves Stomach Decreased gastric secretions

10. 24.13 Three Phases of Gastric Secretion Slide number 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gastric Phase Local reflexes stimulated by stomach distention Distention of the stomach also activates local reflexes that increase stomach secretions (purple arrow). Stomach Distention

11. 24.13 Three Phases of Gastric Secretion Slide number 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. Chyme in the duodenum with a pH less than 2 or containing fat digestion products (lipids) inhibits gastric secretions by three mechanisms. 2. Sensory vagal action potentials to the medulla oblongata (green arrow) inhibit motor action potentials from the medulla oblongata (pink arrow). 3. Local reflexes inhibit gastric secretion (orange arrows). 4. Secretin, gastric inhibitory polypeptide, and cholecystokinin produced by the duodenum (brown arrows) inhibit gastric secretions in the stomach. Intestinal Phase Secretin, gastric inhibitory peptide, cholecystokinin Circulation pH<2 or lipids Local reflexes Decreased gastric secretions Medulla oblongata Vagus nerves Vagus nerves 1 2 3 4

12. 24.13 Three Phases of Gastric Secretion Slide number 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chyme in the duodenum with a pH less than 2 or containing fat digestion products (lipids) inhibits gastric secretions by three mechanisms. pH<2 or lipids Intestinal Phase

13. 24.13 Three Phases of Gastric Secretion Slide number 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intestinal Phase Sensory vagal action potentials to the medulla oblongata (green arrow) inhibit motor action potentials from the medulla oblongata (pink arrow). pH<2 or lipids Medulla oblongata Vagus nerves Vagus nerves Mechanism One Decreased gastric secretions

14. 24.13 Three Phases of Gastric Secretion Slide number 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intestinal Phase Local reflexes inhibit gastric secretion (orange arrows). pH<2 or lipids Local reflexes Decreased gastric secretions Mechanism Two

15. 24.13 Three Phases of Gastric Secretion Slide number 15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Secretin, gastric inhibitory polypeptide, and cholecystokinin produced by the duodenum (brown arrows) inhibit gastric secretions in the stomach. Secretin, gastric inhibitory peptide, cholecystokinin pH<2 or lipids Decreased gastric secretions Circulation Mechanism Three Intestinal Phase