BIOM3200 Unit 12 Notes.docx

BIOM3200 Unit 12 Notes.docx - Unit 12 Digestive Chapter 18...

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Unit 12: Digestive Chapter 18: The Digestive System (p. 612-647) 18.1 INTRODUCTION TO THE DIGESTIVE SYSTEM some digested molecules used for energy (caloric value), the rest used to make additional tissues digestion of polymers into monomers by means of hydrolysis reactions lumen of GI tract continuous with environment (open at both ends) Functions of digestive system: 1. Motility (ingestion, mastication, deglutition, peristalsis and segmentation) 2. Secretion (exocrine [HCL,HCO3, enzymes] and endocrine [hormones] secretions 3. Digestion (breakdown) 4. Adsorption (products to blood or lymph) 5. Storage and elimination 6. Immune barrier Digestive system is the gastrointestinal tract (or alimentary canal) and accessory organs o GI tract is 9m (30ft) long, includes: oral cavity, pharynx, esophagus, stomach, small intestine, large intestine o Accessory organs: teeth, tongue, salivary glands, liver, gallbladder, pancreas Layers of the GI Tract Mucosa o Lines lumen of GI tract o Absorptive/secretory layer (goblet cells secrete mucous) o Simple columnar epithelium supported by lamina propria (thin connective tissue with lymph nodules) o External to lamina propria is muscularis mucosae , thin muscle layer that makes small folds in certain parts of tract Submucosa o Thick, vascular connective tissue layer where absorbed molecules enter blood/lymph o Has glands and submucosal plexus (Meissner’s plexus) which enervates muscularis mucosae Muscularis (muscularis externa) o Causes peristalsis and segmentation o Inner, circular and outer, longitudinal layers of smooth muscle move/pulverize food and mix enzymes o Myenteric plexus (auerbach’s plexus) between muscle layers is the major nerve supply for GI tract (by both para- and sympathetic systems) Serosa o Binding protective layer of areolar connective tissue covered by squamous epithelium Regulation of the GI Tract
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Both para- and sympathetic nerves (by synapsing with submucosal and myenteric plexi) o Parasympathetic stimulate motility and secretions Vagus nerve stimulates esophagus, stomach, pancreas, gallbladder, small intestine, upper large intestine Spinal nerves of sacral region stimulate lower large intestine Sympathetic nerves reduce peristalsis and secretion, contract sphincter muscles ANTAGONISTIC to parasympathetic nerves Rregulated intrinsically (by enteric nervous system or enteric brain is a complex neural network within wall of gut, and paracrine regulators) and extrinsically (by ANS and endocrinesystem) 18.2 FROM MOUTH TO STOMACH Mastication mixes food with saliva (containing antimicrobial agents, salivary amylase) Deglutition has 3 phases (automatic phases controlled by swallowing centre in brain) o Oral: voluntary; creates bolus, muscles push towards back and stimulates next phase o Pharyngeal: automatic; nasopharynx, larynx, vocal cords closed off by soft palate, vocal cords, epiglottis respectively and upper esophageal sphincter relaxes o Esophageal: automatic; peristaltic contractions move bolus to stomach Esophagus
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  • Winter '14
  • Digestive System, Histamine, Clinical Application

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