Understanding Digestive System Mechanisms for Nourishment

1. Chapter 2 The Digestive System: Mechanism for Nourishing the Body 2009 Cengage-Wadsworth

2. Main structures: Oral cavity Esophagus Stomach Small & large intestines Accessory organs: Pancreas Liver Gallbladder The Structures of the Digestive Tract & the Digestive Process 2009 Cengage-Wadsworth

3. The Structures of the Digestive Tract & the Digestive Process • Lumen has 4 main layers: • Mucosa • Epithelium, lamina propria, muscularis mucosa • Submucosa • Connective tissue, lymphoid tissue, submucosal plexus • Muscularis externa • Circular & longitudinal smooth muscle, myenteric plexus • Serosa or adventitia • Connective tissue, visceral peritoneum 2009 Cengage-Wadsworth

4. The Oral Cavity • Mouth & pharynx • Salivary glands • Enzymes in saliva 2009 Cengage-Wadsworth

5. The Esophagus • Moves bolus from oral cavity to stomach • Swallowing • Voluntary, pharyngeal, esophageal • Peristalsis • Gastroesophageal sphincter • Selected diseases & conditions of the esophagus - GERD 2009 Cengage-Wadsworth

6. The Stomach • 4 main regions: • Cardia region • Fundus • Body • Antrum or distal pyloric region • Grinds food & mixes with gastric juices to form chyme • Strong peristalsis for gastric emptying 2009 Cengage-Wadsworth

7. Gastric glands: Cardiac glands Oxyntic glands Pyloric glands Cells in glands: Neck (mucus) cells Parietal (oxyntic) cells Chief (peptic or zymogenic) cells Enteroendocrine cells The Stomach 2009 Cengage-Wadsworth

8. The Stomach • Gastric juice • HCl • Converts pepsinogen to pepsin • Denatures proteins • Releases nutrients from organic complexes • Acts as bacteriocide • Enzymes - pepsin, amylase, lipase • Mucus • Intrinsic factor 2009 Cengage-Wadsworth

9. The Stomach • Regulation of gastric secretions • Hormones & peptides that inhibit gastric secretions • Hormones & neuropeptides that stimulate gastric secretions • Other factors • HCl release stimulated by gastrin, acetylcholine, histamine 2009 Cengage-Wadsworth

10. The Stomach • Selected diseases & conditions of the stomach - peptic ulcers • Regulation of gut motility & gastric emptying 2009 Cengage-Wadsworth

11. The Small Intestine • Structural aspects of the small intestine • Folds of Kerckring - large circular folds of mucosa • Villi - finger-like projections • Microvilli - hair-like extensions of the cells’ plasma membranes • Brush border • Crypts of Lieberkühn 2009 Cengage-Wadsworth

12. The Small Intestine • Regulation of intestinal secretions & motility • Immune system protection of the gastrointestinal tract • Mucosa-associated lymphoid tissue (MALT) • Gut-associated lymphoid tissue (GALT) 2009 Cengage-Wadsworth

13. The Accessory Organs • The pancreas • Digestive enzymes produced by acinar exocrine cells • Pancreatic juice contains: • Bicarbonate • Electrolytes • Pancreatic digestive enzymes • Regulation of pancreatic secretions • Pancreatic digestive enzymes 2009 Cengage-Wadsworth

14. The Accessory Organs • The liver • Consists of lobes made of lobules • Portal circulation • Bile canaliculi 2009 Cengage-Wadsworth

15. The Accessory Organs • The gallbladder • Bile synthesis • Selected conditions/diseases of the gallbladder • Bile storage • The function of bile • The recirculation & excretion of bile • Bile circulation & hypercholesterolemia 2009 Cengage-Wadsworth

16. The Digestive & Absorptive Processes • Digestion • Breaking nutrients down • Occurs in lumen & at brush border • Most digestion & absorption occur in small intestine • Absorption may be by diffusion, facilitated diffusion, active transport, or pinocytosis/ endocytosis 2009 Cengage-Wadsworth

17. The Digestive & Absorptive Processes • Mechanism of absorption depends on: • Solubility (fat vs. water) • Concentration or electrical gradient • Size of molecule • Unabsorbed materials continue to colon 2009 Cengage-Wadsworth

18. The Colon or Large Intestine • Contracts to mix materials • Proximal colonic epithelia absorb Na, Cl, H2O • Materials dehydrated • Intestinal bacteria populations of interest 2009 Cengage-Wadsworth

19. Intestinal Bacteria (Microflora), Pre- and Probiotics, and Disease • Fermentation - breakdown of CHO & protein anaerobically • Generate lactate & short-chain fatty acids, gases • Probiotics - foods containing live bacterial cultures • Prebiotics - food ingredients that promote bacterial growth 2009 Cengage-Wadsworth

20. Intestinal Bacteria (Microflora), Pre- and Probiotics, and Disease • Probiotics are thought to: • Enhance immunity • Prevent colonization by pathogens • Lower pH of the colon • Transform/promote excretion of toxic substances • Enhance fecal bulk 2009 Cengage-Wadsworth

21. Coordination & Regulation of the Digestive Process • Neural regulation • Myenteric plexus - peristalsis, motility • Submucosal plexus - secretions, local blood flow • Regulatory peptides • Hormones • Paracrines 2009 Cengage-Wadsworth

22. Gastrin Cholecystokinin (CCK) Secretin Motilin Glucose-dependent insulinotropic peptide (GIP) Peptide YY Enteroglucagon Amyline Regulatory Peptides 2009 Cengage-Wadsworth

23. Paracrine-acting substances Somatostatin Glucagon-like peptides Insulin-like growth factors Neurocrine peptides Vasoactive intestinal polypeptide (VIP) Gastrin-releasing peptide (GRP) Neurotensin Substance powder (P) Regulatory Peptides 2009 Cengage-Wadsworth

24. Perspective 2 An Overview of Selected Digestive System Disorders with Implications for Nourishing the Body 2009 Cengage-Wadsworth

25. Selected Disorders • Disorder 1: Gastroesophageal reflux cisease • Disorder 2: Inflammatory bowel diseases • Disorder 3: Celiac disease • Disorder 4: Chronic pancreatitis 2009 Cengage-Wadsworth