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Chapter 21c

Chapter 21c. The Digestive System. The Cephalic Phase. Chemical and mechanical digestion begins in the mouth Salivary secretion is under autonomic control Softens and lubricates food Chemical digestion: S alivary amylase and some lipase Saliva also has a protective function

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Chapter 21c

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  1. Chapter 21c The Digestive System

  2. The Cephalic Phase • Chemical and mechanical digestion begins in the mouth • Salivary secretion is under autonomic control • Softens and lubricates food • Chemical digestion: Salivary amylase and some lipase • Saliva also has a protective function • Chewing: mastication

  3. Swallowing Reflex 1 Tongue pushes bolus against softpalate and back of mouth, triggeringswallowing reflex. Soft palate Hard palate Tongue Bolus Epiglottis Glottis Larynx Tonically contracted upperesophageal sphincter Figure 21-24, step 1

  4. Swallowing Reflex 2 Upper esophageal sphincter relaxeswhile epiglottis closes to keepswallowed material out of the airways. Epiglottis Figure 21-24, step 2

  5. Swallowing Reflex 3 Food moves downward into theesophagus, propelled by peristalticwaves and aided by gravity. Figure 21-24, step 3

  6. The Gastric Phase • Storage • Stomach • Digestion • Stomach • Acid, enzymes, and signal molecules • Protection

  7. The Gastric Phase • Activity of secretory cells of the gastric mucosa Gastric mucosa Cell Types Substance Secreted Stimulus for Release Function of Secretion Mucus Tonic secretion;with irritation ofmucosa Physical barrier betweenlumen and epithelium Openingof gastricgland Mucousneck cell Bicarbonate Secreted withmucus Buffers gastric acid toprevent damage toepithelium Activates pepsin;kills bacteria Gastric acid (HCl) Acetylcholine,gastrin, histamine Parietalcells Complexes with vitaminB12 to permit absorption Intrinsic factor Enterochromaffin-like cell Acetylcholine,gastrin Stimulates gastricacid secretion Histamine Pepsin(ogen) Digests proteins Acetylcholine; acid,secretin Chief cells Gastric lipase Digests fats Inhibits gastric acidsecretion Somatostatin Acid in the stomach D cells Acetylcholine,peptidesand amino acids Stimulates gastricacid secretion G cells Gastrin Figure 21-25

  8. The Gastric Phase • Integration of cephalic and gastric phase secretion in the stomach Input viavagus nerve 1 1 Food Gastric mucosa Lumen ofstomach 1 Food or cephalic reflexesinitiate gastric secretion. Entericsensoryneuron Amino acidsor peptides Gastrin stimulates acidsecretion by direct actionon parietal cells or indirectlythrough histamine. 2 G cell Gastrin 2 3 Acid stimulates short reflexsecretion of pepsinogen. D cell Somatostatin + 4 Somatostatin release by H+is the negative feedbacksignal that modulates acidand pepsin release. 4 Negative feedbackpathway ECLcell Histamine Parietalcell H+ Entericplexus 3 Entericsensoryneuron Chiefcell Pepsin Pepsinogen Figure 21-26

  9. The Gastric Phase Input viavagus nerve 1 1 Food Gastric mucosa Lumen ofstomach 1 Food or cephalic reflexesinitiate gastric secretion. Entericsensoryneuron Amino acidsor peptides G cell Gastrin Entericplexus Figure 21-26, step 1

  10. The Gastric Phase Input viavagus nerve 1 1 Food Gastric mucosa Lumen ofstomach 1 Food or cephalic reflexesinitiate gastric secretion. Entericsensoryneuron Amino acidsor peptides Gastrin stimulates acidsecretion by direct actionon parietal cells or indirectlythrough histamine. 2 G cell Gastrin 2 ECLcell Histamine Parietalcell H+ Entericplexus Figure 21-26, steps 1–2

  11. The Gastric Phase Input viavagus nerve 1 1 Food Gastric mucosa Lumen ofstomach 1 Food or cephalic reflexesinitiate gastric secretion. Entericsensoryneuron Amino acidsor peptides Gastrin stimulates acidsecretion by direct actionon parietal cells or indirectlythrough histamine. 2 G cell Gastrin 2 Acid stimulates short reflexsecretion of pepsinogen. 3 ECLcell Histamine Parietalcell H+ Entericplexus 3 Entericsensoryneuron Chiefcell Pepsin Pepsinogen Figure 21-26, steps 1–3

  12. The Gastric Phase Input viavagus nerve 1 1 Food Gastric mucosa Lumen ofstomach 1 Food or cephalic reflexesinitiate gastric secretion. Entericsensoryneuron Amino acidsor peptides Gastrin stimulates acidsecretion by direct actionon parietal cells or indirectlythrough histamine. 2 G cell Gastrin 2 Acid stimulates short reflexsecretion of pepsinogen. 3 D cell Somatostatin + 4 Somatostatin release by H+is the negative feedbacksignal that modulates acidand pepsin release. 4 Negative feedbackpathway ECLcell Histamine Parietalcell H+ Entericplexus 3 Entericsensoryneuron Chiefcell Pepsin Pepsinogen Figure 21-26, steps 1–4

  13. The Gastric Phase • The mucus-bicarbonate barrier of the gastric mucosa Stomachlumen Gastric juice pH ~ 2 The mucus layer is a physical barrier. Mucuslayer Bicarbonate is a chemicalbarrier that neutralizes acid. HCO3– HCO3– pH ~ 7 at cell surface Mucusdroplets Gastricmucouscell Capillary Figure 21-27

  14. Reflexes of Cephalic and Gastric Phases • Long and short reflexes of the cephalic and gastric phases of digestion Figure 12-23

  15. The Intestinal Phase • Chyme in the small intestine inhibits gastric motility and secretion Foodintostomach Acid secretion STOMACH Pepsin and lipase secretion Gastric motility Chymeinto smallintestine Entericnervoussystem SMALLINTESTINE Hyper-osmoticsolution Fats,proteins Acid Carbohydrates ? Endocrine cell Secretin GIP GLP-1 CCK Pancreaticenzymesecretion Pancreaticbicarbonatesecretion Insulinsecretion PANCREAS Figure 21-28

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

  17. The Intestinal Phase • Activation of pancreatic zymogens Lumen of small intestine Pancreatic duct Pancreatic secretions(include inactivezymogens) Trypsinogen ZYMOGENS • Chymotrypsinogen• Procarboxypeptidase• Procolipase• Prophospholipase Enteropeptidasein brush borderactivates trypsin. Trypsin activates ACTIVATED ENZYMES Intestinalmucosa • Chymotrypsin• Carboxypeptidase• Colipase• Phospholipase Figure 21-29

  18. Hepatic Portal System • Most fluid is absorbed in the small intestine Aorta Capillariesof liver Hepaticvein Inferiorvena cava Hepatic artery Liver Capillaries of digestivetract: stomach, intestines,pancreas, and spleen Hepaticportal vein Digestivetract arteries Figure 21-30

  19. 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

  20. The Intestinal Phase: Anatomy of the Large Intestine Intestinalglands Lymphoidnodule Tenia coli Aorta Hepatic portal vein Inferior vena cava Transverse colon Muscularis mucosae Submucosa Ascendingcolon Longitudinal layer(tenia coli) Descendingcolon Muscularisexterna Circular muscle Ileocecal valve Ileum Haustra Cecum Sigmoid colon Appendix Rectum Rectum Internal anal sphincter External anal sphincter Anus Figure 21-31

  21. The Intestinal Phase: Anatomy of the Large Intestine Figure 21-31 (1 of 3)

  22. The Intestinal Phase: Anatomy of the Large Intestine Figure 21-31 (2 of 3)

  23. The Intestinal Phase: Anatomy of the Large Intestine Figure 21-31 (3 of 3)

  24. 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

  25. 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

  26. 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

  27. 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

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

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