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BIO 2401 DIGESTIVE SYSTEM page 1 DIGESTIVE SYSTEM Functions of the Digestive System 1. ingestion – taking of food into digestive tract, usually via mouth 2. propulsion – moving of food through alimentary canal; includes swallowing and peristalsis peristalsis – means of propulsion involving alternating waves of contraction and relaxation 3. digestion – breaking down of food into very small particles; several parts mechanical digestion – physically prepares food for chemical digestion by enzymes chewing – mixing of food with saliva while teeth grind it churning – mixing of food with stomach enzymes segmentation – rhythmic local constrictions of intestines that allow mixing of food with digestive juices chemical digestion – catabolic steps involved in breakdown of food molecules; accomplished by digestive enzymes 4. absorption – passage of digestive end products from lumen of gut into blood or lymph 5. defecation – elimination of indigestible substances from body via anus Major Structure of the Digestive System ± Alimentary canal (gastrointestinal tract) 1. mouth (oral cavity, buccal cavity) – ingestion/food entry 2. pharynx – propulsion of food into esophagus 3. esophagus – propulsion of food into stomach 4. stomach – storage of food and initial chemical breakdown 5. small Intestine – major digestive organ; absorption of food molecules 6. large Intestine – absorption of water 7. anus – propulsion of indigestible food out of body ± Accessory Organs 1. teeth – mechanical digestion 2. salivary glands – digestive enzymes 3. pancreas – digestive enzymes 4. liver – fat emulsification 5. gall bladder – storage of bile made by liver for later emulsification of fat Basic Histology of the Alimentary Canal Wall 1. mucosa – moist epithelium; lines lumen of GI tract from mouth to anus; secretes mucus, digestive enzymes, hormones; absorbs end products; protects; has 3 linings or sublayers 2. submucosa – dense connective tissue containing blood and lymph vessels, lymph nodules, and nerve fibers 3. muscularis externa – responsible for segmentation and peristalsis; has inner circular layer and outer longitudinal layer of smooth muscle cells 4. serosa or adventitia – serosa = visceral peritoneum; areolar connective tissue; adventita = fibrous connective tissue; all retroperitoneal organs have both layers
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BIO 2401 DIGESTIVE SYSTEM page 2 Mouth and Its Accessory Organs 1. mouth (oral cavity, buccal cavity) ± histology: stratified squamous epithelium, except on gums, hard palate, tongue dorsum (these are keratinized); bound by lips anteriorly, cheeks laterally, palate superiorly, tongue inferiorly ± functions: ingestion: intake of food mechanical digestion: chewing of food chemical digestion: enzymatic breakdown of food 2. teeth (will be covered in lab) – grinding of food incisors – blade shaped; function in clipping and cutting cuspids (canines) – conical with sharp ridgeline and pointed tip; function in tearing and slashing bicuspids
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