Transcript Chapter 1
Chapter 2 The Digestive System: Mechanism for Nourishing the Body 2009 Cengage-Wadsworth The Structures of the Digestive Tract & the Digestive Process • Main structures: – – – – Oral cavity Esophagus Stomach Small & large intestines • Accessory organs: – Pancreas – Liver – Gallbladder 2009 Cengage-Wadsworth 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 The Oral Cavity • Mouth & pharynx • Salivary glands • Enzymes in saliva 2009 Cengage-Wadsworth 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 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 The Stomach • Gastric glands: – Cardiac glands – Oxyntic glands – Pyloric glands • Cells in glands: – Neck (mucus) cells – Parietal (oxyntic) cells – Chief (peptic or zymogenic) cells – Enteroendocrine cells 2009 Cengage-Wadsworth 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 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 The Stomach • Selected diseases & conditions of the stomach - peptic ulcers • Regulation of gut motility & gastric emptying 2009 Cengage-Wadsworth 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 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 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 The Accessory Organs • The liver – Consists of lobes made of lobules – Portal circulation – Bile canaliculi 2009 Cengage-Wadsworth 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 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 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 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 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 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 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 Regulatory Peptides • Gastrin • Cholecystokinin (CCK) • Secretin • Motilin • Glucosedependent insulinotropic peptide (GIP) • Peptide YY • Enteroglucagon • Amyline 2009 Cengage-Wadsworth Regulatory Peptides • 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) 2009 Cengage-Wadsworth Perspective 2 An Overview of Selected Digestive System Disorders with Implications for Nourishing the Body 2009 Cengage-Wadsworth Selected Disorders • Disorder 1: Gastroesophageal reflux cisease • Disorder 2: Inflammatory bowel diseases • Disorder 3: Celiac disease • Disorder 4: Chronic pancreatitis 2009 Cengage-Wadsworth