The Digestive System: Mechanism for Nourishing the Body 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: Cells in 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 Enzymes - pepsin, amylase, lipase Mucus 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 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 Glucose-dependent insulinotropic peptide (GIP) Peptide YY Enteroglucagon Amyline 2009 Cengage-Wadsworth

Regulatory Peptides Paracrine-acting substances Neurocrine peptides 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