139 13F Digestive System - Digestive System Bio 139 Fall...

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Digestive System Bio 139 Fall 2013 Dr. Michael W. Thompson
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Functions of the digestive system Processing of food into usable chemical substances Absorption of usable nutrients Elimination of wastes Barrier (innate immune system) stomach acid, other secretions of digestive tract kill most microorganisms
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General histology Four layers (innermost to outermost) Mucosa (3 sub-layers) mucous epithelium lamina propria muscularis mucosae Submucosa Muscularis (2 sub-layers; 3 in stomach) Serosa or adventitia
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General histology
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The oral cavity Contains teeth, tongue that are involved in mastication (chewing) of food Tongue is controlled by intrinsic and extrinsic (attached to hyoid bone) muscles holds food in for chewing assists in swallowing Oral cavity lined mostly with stratified squamous epithelium (non-keratinized, except for lips)
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Mastication Anterior teeth (incisors, canines) cut and tear; posterior (premolars and molars) crush and grind Increases efficiency of digestion by breaking up the food larger surface area available for digestive enzymes to work on Four pairs of muscles assist temporalis masseter medial and lateral pterygoids
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Mastication Saliva is added moistens food for easier swallowing begins digestion process contains amylase, which breaks down some starches also contains lysozyme (weak antibacterial enzyme) and some antibodies Secreted by several glands: parotids (in front of ear on each side) submandibular sublingual
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Salivary glands
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The esophagus Leads from pharynx to stomach Lies within mediastinum; passes through diaphragm Lined with stratified squamous epithelium Differs slightly in the histology – some skeletal (voluntary) muscle in upper portion UES (upper esophageal sphincter) and LES (lower) control entry and exit of food Mucus glands in submucosa make copious amounts of mucus that lubricate the lining of the esophagus
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Swallowing Three phases buccal bolus of food from mouth is pushed by tongue against hard palate, forcing it into oropharynx pharyngeal a reflex stimulated by receptors in oropharynx mediated by medulla oblongata soft palate elevated, closing passage between naso- and oropharynx constrictor muscles contract in sequence, pushing bolus towards esophagus (skeletal muscles under involuntary control) UES relaxes to allow food into esophagus epiglottis and vestibular folds cover opening into larynx
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Swallowing Three phases esophageal muscular contractions occur in peristaltic waves pushes food downwards Flattens out, diffuses bolus for easier entry into stomach peristaltic contractions cause LES to relax as food approaches LES normally remains closed to prevent regurgitation of stomach contents defects in this called gastroesophageal reflux disorder (GERD)
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Swallowing
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Peristalsis in the esophagus
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Stomach
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