The Gastric Phase

1. The Gastric Phase • Storage • Stomach stores food and controls its passage into the small intestine • Digestion • Stomach • Chemical: Acid, enzymes, and signal molecules • Mechanical • Protection • Stomach acid destroys many bacteria and other pathogens. Stomach protects itself w/thick mucus

2. The Gastric Phase Activity of secretory cells of the gastric mucosa Figure 21-25

3. The Gastric Phase Input via vagus nerve 1 1 Food Food or cephalic reflexes initiate gastric secretion. 1 Gastric mucosa Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. Enteric sensory neuron Amino acids or peptides 2 G cell Gastrin Lumen of stomach 3 Acid stimulates short reflex secretion of pepsinogen. 2 Somatostatin D cell + Somatostatin release by H+ is the negative feedback signal that modulates acid and pepsin release. 4 4 Negative feedback pathway Enterochromaffin-like cell Histamine KEY Parietal cell H+ Stimulus Enteric plexus Enteric sensory neuron 3 Receptor Integrating center Chief cell Pepsinogen Pepsin Efferent pathway Integration of cephalic and gastric phase secretion in the stomach Figure 21-26

4. The Gastric Phase Input via vagus nerve 1 1 Food Food or cephalic reflexes initiate gastric secretion. 1 Gastric mucosa Enteric sensory neuron Amino acids or peptides G cell Gastrin Lumen of stomach KEY Stimulus Enteric plexus Receptor Integrating center Efferent pathway Figure 21-26, step 1

5. The Gastric Phase Input via vagus nerve 1 1 Food Food or cephalic reflexes initiate gastric secretion. 1 Gastric mucosa Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. Enteric sensory neuron Amino acids or peptides 2 G cell Gastrin Lumen of stomach 2 ECL cell Histamine KEY Parietal cell H+ Stimulus Enteric plexus Receptor Integrating center Efferent pathway Figure 21-26, steps 1–2

6. The Gastric Phase Input via vagus nerve 1 1 Food Food or cephalic reflexes initiate gastric secretion. 1 Gastric mucosa Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. Enteric sensory neuron Amino acids or peptides 2 G cell Gastrin Lumen of stomach 3 Acid stimulates short reflex secretion of pepsinogen. 2 ECL cell Histamine KEY Parietal cell H+ Stimulus Enteric plexus Enteric sensory neuron 3 Receptor Integrating center Chief cell Pepsinogen Pepsin Efferent pathway Figure 21-26, steps 1–3

7. The Gastric Phase Input via vagus nerve 1 1 Food Food or cephalic reflexes initiate gastric secretion. 1 Gastric mucosa Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. Enteric sensory neuron Amino acids or peptides 2 G cell Gastrin Lumen of stomach 3 Acid stimulates short reflex secretion of pepsinogen. 2 Somatostatin D cell + Somatostatin release by H+ is the negative feedback signal that modulates acid and pepsin release. 4 4 Negative feedback pathway ECL cell Histamine KEY Parietal cell H+ Stimulus Enteric plexus Enteric sensory neuron 3 Receptor Integrating center Chief cell Pepsinogen Pepsin Efferent pathway Figure 21-26, steps 1–4

8. The Gastric Phase The mucus-bicarbonate barrier of the gastric mucosa Figure 21-27

9. The Intestinal Phase The effects of intestinal-phase events on gastric function Figure 21-28

10. The Intestinal Phase • Bicarbonate neutralizes gastric acid • Goblet cells secrete mucus for protection and lubrication • Bile • Fat digestion • Digestive enzymes • Enteropeptidase

11. Activation of Pancreatic Zymogens Figure 21-29

12. Hepatic Portal System Most fluid is absorbed in the small intestine Figure 21-30

13. The Intestinal Phase • Most digestion occurs in small intestine • Large intestine concentrates waste for excretion • Motility in large intestine • Mass movement triggers defecation • Defecation reflex • Digestion and absorption in large intestine • Diarrhea can cause dehydration

14. Anatomy of the Large Intestine Figure 21-31

15. Anatomy of the Large Intestine Figure 21-31a

16. Anatomy of the Large Intestine Figure 21-31b

17. Anatomy of the Large Intestine Figure 21-31c

18. Immune Function • M cells sample the contents of the gut • Immune cells secrete cytokines • Cytokines trigger inflammatory response • Increase in Cl–, fluid, and mucus secretion • Vomiting is a protective reflex

19. Summary • Function and processes • Digestion, absorption, motility, secretion, and GALT • Anatomy • Motility • Tonic and phasic contractions • Slow wave potentials, interstitial cells of Cajal, migrating motor complex, peristaltic contractions, and segmental contractions

20. Summary • Secretion • Parietal cells, CFTR chloride channel, mucous cells, goblet cells, saliva, and bile salts • Regulation • Short reflexes, ENS, long reflexes, intrinsic neurons, gastrin family, secretin family, and other hormones

21. Summary • Digestion and absorption • Amylase, disaccharidases, endopeptidases, exopeptidases, lipase, colipase, micelles, chylomicrons, and intrinsic factor • The cephalic phase • The gastric phase • Mucous cells, chief cells, D cells, ECL cells, and G cells

22. Summary • The intestinal phase • Brush border, mass movement, and defecation reflex • Immune functions • M cells and vomiting