Chapter 24 Lecture Notes

Chapter 24 Lecture Notes - Chapter 24 Digestive System...

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1 Chapter 24 Digestive System Overview of the Digestive System Digestive tract or alimentary canal – Continuous tube in the ventral body cavity – Extend form the mouth to the anus. Include: h Mouth h Pharynx h Esophagus h Stomach h Small intestine h Large intestine h Anus Accessory digestive organs – Directly or indirectly contact food h Teeth h Tongue h Salivary glands h Liver h Gall bladder h Pancreas
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2 Functions of the Digestive System 1. Ingestion Ingestion of food and liquid Voluntary and active process 2. Secretion: Water, acid, buffers, enzymes, and salts by GI tract and glands 3. Mixing and propulsion : Motility mix and move materials along the tract 4. Digestion : Mechanical: grinding (teeth), churning (stomach) Chemical: enzymes 5. Absorption of Nutrients, ions, water, vitamins 6. Defecation : Elimination of waste The Digestive Process h Ingestion h Propulsion h Mechanical Digestion h Chemical Digestion h Absorption h Defecation
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3 Layers of The GI Tract • From the lower esophagus to the anal canal the GI tract has four layers from deep to superficial: Mucosa Submucosa Muscularis externa Serosa Mucosa 1. Epithelium:( renew every 5-7 days) – Nonkeratinized stratified squamous epithelium in mouth, pharynx, esophagus, anal canal; a protective function – Simple columnar (secretion and absorption) contain goblet cells, in stomach, small and large intestine • Firmly sealed by tight junctions to restrict leakage between cells • Enteroendocrine cells located among epithelium and secret hormones 2. Lamina propria : – Areolar connective tissue support and bind epithelium to muscularis mucosae – Contains blood vessels, lymphatic vessels, sensory nerve endings – Contains secretory cells of mucus glands in oral cavity, pharynx, esophagus, stomach, and duodenum – Contain mucosa-associated lymphatic tissue (MALT): • Present along the GI tract especially tonsils and appendix • Immune response against invaders 3. Muscularis mucosae : – Narrow band of smooth muscles and elastic fibers – throws mucus membrane of stomach and small intestine into folds to increase surface area – Muscularis movement ensure all absorptive cells fully exposed to GI content
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4 Basic Alimentary Tract Structure Submucosa Dens irregular connective tissue surround the muscularis mucosa Bind mucosa to muscularis Contain large blood vessels and lymphatics that receives food molecules May contain exocrine glands (secrete enzymes and buffers) and lymphatic tissue Contain submucosal plexus( plexus of meissner part of the enteric nervous system, ENS) – innervate the mucosa and submucosa – regulate mucosal movement, vasoconstriction of blood vessels, and control secretion – Contains: • Sensory neurons • Parasympathetic ganglionic neurons • Sympathetic postganglionic neurons
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5 Muscularis Externa Smooth muscle – inner circular and outer longitudinal – For mechanical processing
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Chapter 24 Lecture Notes - Chapter 24 Digestive System...

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