CHAPTER 24 - CHAPTER 24 DIGESTIVE SYSTEM Digestion breaking...

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CHAPTER 24 DIGESTIVE SYSTEM Digestion – breaking down of food into molecules small enough to enter body cells FIGURE 24.1 p 853 - very general diagram of organs in digestion Organs of digestion are divided into 2 groups A. Gastrointestinal (GI) tract (alimentary canal)- continuous tube passing through the ventral body cavity from mouth to anus. The GI tract contains the food while it is in the body, until it is either absorbed or eliminated. Total length is about 30 feet. 1. Mouth 2. Pharynx 3. Esophagus 4. Stomach 5. Small intestine (SI) 6. Large intestine (LI) B. Accessory structures 1. Teeth – chewing 2. Tongue – handling food and swallowing 3. Salivary glands 4. Liver Produce or store secretions, add them to GI 5. Gallbladder tract through ducts, never touch food 6. Pancreas Gastroenterology – structure, function, diagnosis, and treatment of diseases of the stomach and intestines Gastro – stomach Entero – intestines 6 basic activities of the digestive system 1. Ingestion – taking in food 2. Secretion – 7 liters/day – water, acid, buffers, enzymes 3. Movement of food along the GI tract (propulsion)
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4. Digestion – mechanical and chemical breakdown a. Mechanical digestion – chewing, mixing, etc b. chemical digestion – splitting of ingested carbohydrate, protein, and lipid molecules into smaller molecules that can be absorbed and used by cells 5. Absorption – passage of digested food into the cardiovascular or lymphatic systems for distribution to cells 6. Defecation – elimination of indigestible material (feces) LAYERS OF THE GI TRACT WALL The wall of the GI tract from esophagus to anus has the same 4 basic layers: 1. Mucosa – mucous membrane that lines the GI tract a. Epithelium – next to food 1) non-keratinized stratified squamous – mouth, pharynx, esophagus, anal canal – protection 2)simple columnar – rest of tract, absorption and secretion b. CT layer called the lamina propria – support, provides blood supply and contains many immune cells. The lymphatic tissue of this area is called the mucosa-associated lymphoid tissue (MALT) c. Muscularis mucosae – very thin layer of smooth muscle, helps form the ridges and folds of the mucosa 2. Submucosa – areolar CT that binds the mucosa to the third layer and contains the submucosal plexus (plexus of Meissner), part of the enteric nervous system concerned with control of secretion, vasomotor nerves, and the muscularis mucosae. This layer may also contain glands and lymphatic tissue. 3. Muscularis a. Skeletal muscle of the mouth, pharynx, and upper esophagus aids in chewing and swallowing b. Skeletal muscle of the anal canal (external sphincter) permits voluntary control of defecation c. Smooth muscle throughout the rest of the tract – contractions help break down food, mix it with digestive secretions and propel it along the GI tract, 2 layers: 1) Inner sheet of circular fibers 2) Outer sheet of longitudinal fibers d. Also contains the other ENS nerve plexus, the myenteric plexus of Auerbach, which is the major control of GI tract motility
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4. Serosa – outermost layer – serous membrane of simple squamous epithelium (mesothelium) and CT.
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This note was uploaded on 07/24/2011 for the course BSC 1094 taught by Professor Porter during the Fall '11 term at Edison State College.

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CHAPTER 24 - CHAPTER 24 DIGESTIVE SYSTEM Digestion breaking...

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