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Chapter 24 The Digestive System Lecture Outline Digestive system 1. Alimentary canal / Gastrointestinal tract / Digestive tract oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus 2. Accessory organs teeth, tongue, salivary glands, liver, gallbladder, pancreas Functions 1. ingestion 2. propulsion peristalsis 3. mechanical processing 4. chemical digestion 5. secretion 6. absorption 7. excretion defecation: feces Control 1. Neural: Enteric Nervous System A. Short reflexes: ENS B. Long reflexes: ENS + ANS 2. Hormonal enteroendocrine cells 3. Local prostaglandins histamine Location Peritoneal cavity Parietal peritoneum Visceral peritoneum Peritoneal fluid Ascites Peritonitis Mesenteries Peritoneal organs Retroperitoneal organs Lesser omentum Falciform ligament Greater omentum Blood supply Hepatic portal circulation Histology 1. Mucosa A. Epithelium goblet cells stratified squamous epithelium simple columnar epithelium B. Lamina propria areolar connective tissue MALT tonsils C. Muscularis mucosae Amy Warenda Czura, Ph.D. 2. Submucosa dense irregular connective tissue exocrine glands Submucosal Nerve plexus 3. Muscularis externa smooth muscle sphincters Myenteric Nerve Plexus 4. Serosa or Adventitia serosa = visceral peritoneum, mesothelium adventitia = dense irregular C.T. Movement peristalsis segmentation ENS ANS parasympathetic = ↑ activity sympathetic = ↓ activity Anatomy and Physiology 1. Oral cavity Structure stratified squamous epithelium cheeks tongue hard palate soft palate Functions: 1. analyze (taste buds) 2. process (chew) 3. lubricate (saliva) 4. digest (amylase) Accessory organs A. Tongue papillae taste buds Functions: 1. speech 2. manipulate 3. compress bolus 4. analyze 5. secretions a. mucin b. lingual lipase B. Salivary glands Saliva: -water -enzymes (amylase) -buffers -mucin -antibodies (IgA) -antimicrobials (lysozyme, defensins) Functions: 1. cleanse 2. dissolve 1 SCCC BIO132 Chapter 24 Handout 3. moisten 4. digestion 5. buffer Glands: 1. Parotid 2. Sublingual 3. Submandibular dry mouth C. Teeth mastication Pulp cavity Dentin Odontoblasts Crown Enamel hydroxyapatite Root Cementum Periodontal ligaments Alveolus Types: 1. Incisors 2. Cuspids 3. Bicuspids 4. Molars Wisdom teeth 20 deciduous teeth 32 permanent teeth Impacted tooth Dental caries Periodontal disease 2. Pharynx Oropharynx Laryngopharynx stratified squamous epithelium tonsils 3. Esophagus Gastroesophageal sphincter Gastroesophageal reflux disease (Heart burn) Features: 1. stratified squamous epithelium 2. lumen folds 3. esophageal glands 4. skeletal muscle 5. adventitia Deglutition 1. Buccal phase 2. Pharyngeal phase 3. Esophageal phase 4. Stomach Functions: 1. storage 2. mechanical breakdown 3. chemical breakdown 4. intrinsic factor: Vitamin B12 Chyme Amy Warenda Czura, Ph.D. Regions: 1. Cardia gastroesophageal sphincter gastric glands: mucus 2. Fundus 3. Body gastric glands: acid + enzyme 4. Pyloric region pyloric sphincter gastric glands: hormones Histology Rugae Oblique muscle simple columnar epithelium Goblet cells Gastric pits gastric glands Gastric glands Cardia mucus Fundus & Body 1. Parietal cells A. intrinsic factor B. H+ & Cl-kill microbes -denature proteins -digestion -activate pepsin 2. Chief cells A. pepsinogen → pepsin B. rennin Pyloric 1. G cells gastrin 2. D cells somatostatin Gastritis Peptic ulcer Helicobacter pylori Regulation: 1. ANS 2. ENS 3. Hormones Phases: 1. Cephalic phase parasympathetic secretions Gastrin 2. Gastric phase A. Neural response ANS + ENS Parietal & Chief cells G cells B. Hormonal response Gastrin Parietal and Chief cells 2 SCCC BIO132 Chapter 24 Handout motility C. Local response Histamine Parietal cells 3. Intestinal phase A. Neural response Enterogastric reflex B. Hormonal response 1. lipids Cholecystokinin Gastric Inhibitory Peptide 2. acid pH Secretin 3. proteins Gastrin 5. Small intestine A. Duodenum Pyloric sphincter Duodenal ampula Hepatopancreatic sphincter B. Jejunum C. Ileum Peyers patches Ileocecal valve Histology 1. Plicae 2. Villi 3. Microvilli: brush border Lacteals Glands 1. Goblet cells 2. Intestinal glands in crypts A. Intestinal juice B. Lysozyme C. Hormones Intestinal gastrin Cholecystokinin Secretin Gastric Inhibitory Peptide Vasoactive Intestinal Peptide Somatostatin D. Epithelial cells Brush border enzymes 3. Duodenal glands Secretion Parasympathetic Enterocrinin Intestinal movements Myenteric reflexes: ENS Gastroenteric reflex: ANS Gastroileal reflex: ANS Emesis reflex Emetic center: medulla oblongata 6. Pancreas A. Pancreatic islets Insulin Amy Warenda Czura, Ph.D. Glucagon B. Pancreatic acini Pancreatic juice enzymes + buffers 1. Secretin 2. Cholecytokinin Enzymes: proenzymes 1. Pancreatic alpha amylase 2. Pancreatic lipase 3. Nucleases 4. Proteolytic enzymes a. Proteases b. Peptidases Enterokinase Trypsinogen Trypsin Pancreatitis Diabetes mellitus 7. Liver Lobes Left Right Caudate Quadrate Falciform ligament Ligamentum teres Lobules Interlobular septa Central vein Portal triad Hepatic artery Hepatic portal vein Bile duct Hepatocytes Sinusoids Kupffer cells 1. pathogens & debris 2. iron 3. lipids 4. heavy metals Bile pathway: Bile canaliculi Bile duct Common hepatic duct Cystic duct Common bile duct Ampula Hepatopancreatic sphincter Liver functions: 1. Metabolic regulation 2. Hematological regulation A. blood reservoir B. phagocytosis & antigen presentation C. hormones D. antibodies E. toxins 3 SCCC BIO132 Chapter 24 Handout F. plasma proteins 3. Bile synthesis Components water, electrolytes bilirubin cholesterol phospholipids bile salts Emulsification Enterohepatic circulation Secretin Hepatitis Cirrhosis 8. Gallbladder Bile Cholecystokinin Gall stones Cholecystitis Secretion and Absorption in Small Intestine 1. Neural A. ANS sympathetic parasympathetic 2. Hormones of duodenum A. Enterocrinin B. Intestinal gastrin C. Gastric inhibitory peptide D. Secretin E. Cholecystokinin F. Vasoactive Intestinal Peptide G. Somatostatin 9. Large intestine Functions: 1. absorb water 2. absorb vitamins & electrolytes 3. store, compact feces & defecation Bacteria Vitamin K Biotin Vitamin B5 Stercobilins & urobilins Fermentation products Flatus Histology Teniae coli Haustra Intestinal glands Lymphoid nodules: MALT Simple columnar epithelium Goblet cells Subdivisions A. Cecum Ileocecal valve Appendix Appendicitis B. Colon Amy Warenda Czura, Ph.D. 1. Ascending 2. Transverse 3. Descending 4. Sigmoid Diverticulitis C. Rectum Anal canal Internal anal sphincter External anal sphincter Movements 1. Haustral contractions 2. Mass movements 3. Defecation reflex Diarrhea Constipation Chemical digestion Hydrolysis Carbohydrate Amylases: tri-, disaccharides Brush border enzymes: monosaccharides Facilitated diffusion & Cotransport Lactose intolerant Lipids Lipases: monoglycerides & fatty acids Micelles with bile salts Chylomicrons Lacteals Protein Pepsin + acid: polypeptides Proteases & peptidases: amino acids Facilitated diffusion & Cotransport Nucleic acids Nucleases: nucleotides Brush border enzymes: nitrogenous bases, pentose sugar, phosphate ions Active transport Water Osmosis Ions Na+, Ca++, K+, Mg++, Fe++, Cl-, I-, HCO3Diffusion, Cotransport, Active transport Vitamins Fat soluble (A,D, E, K): chylomicrons Water soluble (B, C): diffusion Vitamin B 12: intrinsic factor Age ↓ cell division ↑ ulcer ↓ smooth muscle function ↑ constipation ↑ diverticulitis ↑ hemorrhoids ↑ gastroesophageal reflux disease ↑ damage, ↑ cancer 4 SCCC BIO132 Chapter 24 Handout Digestive System Alimentary canal / Gastrointestinal tract (G.I.): Accessory digestive organs: Oral cavity Teeth Pharynx Tongue Esophagus Salivary glands Stomach Liver Small intestine Gallbladder Large intestine Pancreas Rectum Anus Amy Warenda Czura, Ph.D. 5 SCCC BIO132 Chapter 24 Handout Histology of G.I. 1. Mucosa (Mucous membrane) Functions to secrete mucus, digestive enzymes, and hormones, to absorb end products of digestion, and provide protection from pathogens A. Epithelium (continuously renewed, surface cells last only 2-6 days) Stratified squamous: oral cavity, pharynx, esophagus, anus Simple columnar: stomach, intestine: has goblet cells (mucus) and enteroendocrine cells (hormones) B. Lamina propria Loose areolar connective tissue with blood vessels, lymphatic vessels, nerves, mucous glands and lymphoid tissue (extending from submucosa): MALT (mucosa associated lymphatic tissue e.g. Peyer’s patches) or tonsils C. Muscularis mucosae Bands of smooth muscle and elastic fibers: one layer circumferential one longitudinal Functions to change shape of plicae and villi Villi: finger-like projections of the mucosa layer; increase surface area Plicae (small intestine): folds of mucosa and submucosa; increase surface area Rugae (stomach): pleats of mucosa and submucosa; expand to accommodate volume 2. Submucosa Dense irregular connective tissue, contains large vessels, glands to secrete digestive enzymes and mucus, houses the Submucosal Nerve Plexus (autonomic nervous system control of glands and smooth muscle of mucosa) 3. Muscularis Externa Consists of inner circular layer and outer longitudinal layer of smooth muscle for mixing and moving lumenal contents, circular layer thickened to create sphincters at junctions to prevent backflow Contains the Myenteric Nerve Plexus to control G.I. mobility via local reflex arcs and ANS stimulation 4. Serosa or Adventitia Serosa = visceral peritoneum: areolar connective tissue plus mesothelium, covers all abdominal / peritoneal G.I. tract organs Adventitia = dense irregular connective tissue, anchors organs to surrounding tissues, covers oral cavity, pharynx, esophagus, and rectum Amy Warenda Czura, Ph.D. 6 SCCC BIO132 Chapter 24 Handout Regulation of gastric activity Prepares stomach for food Triggered by seeing, smelling, or thinking of food Lasts a few minutes Neural response: parasympathetic ANS triggers increase in all gastric secretions (mucus, enzymes, acid) and triggers G cells to release Gastrin (causes secretion and motility) Initiates stomach digestive activities Triggered by food entering stomach (stimuli = distension, peptides, low acidity) Lasts 3-4 hours (Three responses:) Neural response: stretch receptors activate ENS reflexes and parasympathetic ANS innervation, both stimulate secretions from parietal cells (acid), Chief cells (pepsin) and G cells (Gastrin) *(Sympathetic stimulation shuts down gastric secretion via somatostatin from D cells) Hormonal response: triggered by neural response, peptides and increased pH, G cells release Gastrin which trigger secretion by parietal and chief cells and also gastric mobility Local response: triggered by distortion, Mast cells release histamine which stimulates parietal cells Controls chyme entry into duodenum Triggered by chyme entering duodenum Lasts many hours *Greatest acid production via 3-fold stimulation of parietal cells: 1. Ach from ENS & parasympathetic ANS 2. Gastrin from G cells 3. Histamine from Mast cells Involves excititory and inhibitory control of gastric activity depending on chyme composition Neural response: stretch receptors trigger Enterogastric Reflex which turns off ENS and parasympathetic stimulation of G cells and stimulates sympathetic stimulation of pyloric sphincter (contracts) Hormonal responses: (different hormones depending on chyme composition): Lipids, carbohydrates, peptides → Cholecystokinin and Gastric Inhibitory Peptide: inhibit gastric secretion and motility (also stimulates pancreas + gallbladder secretion) Low pH → Secretin: inhibits gastric secretion (also stimulates pancreas and liver secretion) Proteins → Intestinal Gastrin: stimulates parietal and chief cells, stimulates gastric mobility Amy Warenda Czura, Ph.D. 7 SCCC BIO132 Chapter 24 Handout Coordination of Secretion and Absorption in the Small Intestine: 1. Neural Mechanisms A. ANS: parasympathetic = increase digestive activity sympathetic = decrease digestive activity B. ENS reflexes: coordinate movement of materials from one region to next 2. Hormonal Mechanisms Hormones from intestinal glands of duodenum control small intestine, stomach, and accessory organs to coordinate digestive activities A. Enterocrinin: released when chyme enters duodenum, stimulates mucus production in duodenum B. Intestinal Gastrin: released when chyme contains protein, stimulates gastric activity (“activity” = secretion and motility) C. Gastric Inhibitory Peptide: released when chyme contains lipids and carbohydrates, inhibits gastric activity D. Secretin: released when chyme is acidic, stimulates release of bile from liver and buffers from pancreas, and reduces gastric activity E. Cholecystokinin: released when chyme contains lipids and peptides, stimulates: -secretion of enzymes from pancreas, -contraction of gallbladder for bile release -relaxes hepatopancreatic sphincter to allow entry of bile and enzymes into duodenum -inhibits gastric activity -reduces hunger sensation (20min post food consumption) F. Vasoactive Intestinal Peptide: released when chyme enters duodenum, inhibits gastric secretion, stimulates intestinal secretion, dilates local capillaries for absorption G. Somatostatin: released in response to sympathetic stimulation, -inhibits gastric activity -inhibits secretion from pancreas and gallbladder -inhibits blood flow to intestine thus inhibiting absorption Amy Warenda Czura, Ph.D. 8 SCCC BIO132 Chapter 24 Handout Amy Warenda Czura, Ph.D. 9 SCCC BIO132 Chapter 24 Handout Substance Digestion Method Absorption Method Carbohydrates Amylases (saliva, pancreas): polysaccharides → di- and trisaccharides Brush Border Enzymes (small intestine): di- and trisaccharides → monosaccharides………………... Facilitated diffusion or Cotransport of monosaccharides Lipids Bile salts (liver): emulsification Lipases (tongue, pancreas) triglycerides → monoglycerides and fatty acids…………... Micelles form: monoglycerides, fatty acids and bile salts Micelles absorbed by intestinal epithelium, proteins added = chylomicron (water soluble) Chylomicrons exocytosed into lumen Chylomicrons absorbed by lacteal Proteins Mastication (mouth) Churning (stomach) Pepsin + Acid (stomach) protein → polypeptide Proteases + Peptidases (pancreas, brush border) polypeptide → amino acids……………………………….. Facilitated diffusion or Cotransport of amino acids Nucleic Acids Nucleases (pancreas) nucleic acid → nucleotides Brush Border Enzymes (small intestine) nucleotides → nitrogenous bases + sugar + phosphate ions Active transport of nitrogenous bases + sugar + phosphate ions Water No digestion required Osmosis (95% in small intestine) 2L from food, 7L from secretions (~150ml lost in feces) Ions No digestion required Na+, Ca++, K+, Mg++, Fe++, Cl-, I-, HCO3Diffusion, Cotransport, Active Transport Vitamins No digestion required Fat soluble: A, D, E, K…………………………………….. Mixed with fats in micelle → chylomicrons (fat soluble) Water soluble: most B vitamins, C………………………... Diffusion (water soluble) Vitamin B12………………………………. Bound to intrinsic factor, binds receptors, endocytosed (B12) Digestion And Absorption Summary of all the hormones involved in digestion: Amy Warenda Czura, Ph.D. 10 SCCC BIO132 Chapter 24 Handout