CHAPTER 26 Digestive System


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CHAPTER 26: DIGESTIVE SYSTEM I. GENERAL STRUCTURE AND FUNCTIONS OF THE DIGESTIVE SYSTEM A. Basics i. Bolus , then chyme (paste like substance produced by the stomach) ii. 2 categories of organs: 1. Digestive organs (6) A. Collectively make the gastrointestinal (GI) track (digestive tract; alimentary canal). B. Forms a continuous tube from mouth to anus C. Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine 2. Accessory digestive organs (6) A. Connected to the GI tract, but not a part of it. Helps GI tract digest material. B. Teeth, tongue, salivary glands, liver, gallbladder, pancreas B. Digestive system functions (6) i. Ingestion—introduction of food in the oral cavity. (1 st step) ii. Digestion—breakdown. 2 aspects: 1. Mechanical digestion—physical breakdown A. Mastication —chewing ingested material in oral cavity. First part of mechanical digestion. 2. Chemical digestion—uses enzymes iii. Propulsion—how they move through the GI. 2 types of movement involved: 1. Peristalsis —wave of muscular contractions of GI tract to move material (toothpaste analogy) 2. Segmentation —churning/mixing movements via contraction and relaxation of GI tract. Helps disperse material and mixes it w/ enzyme secretions and mechanically breaks down. iv. Secretion—producing and releasing mucin or fluids (bile, acid, digestive enzymes) 1. Mucin mixes w water to coat and protect the GI wall. (against acidic secretions and abrasions) 2. Bile, acid, enzymes help digest v. Absorption—passive movement or active transport of electrolytes, digestion products, vitamins, and water across GI epithelium and into GI blood and lymph vessels. vi. Elimination—indigestible materials (ex: cellulose, fiber) and waste products (secreted by accessory organs) compacted into feces, then eliminated via defecation. II. ORAL CAVITY A. Basics i. Mouth = entrance to GI ii. Initial place of mechanical and chemical digestion (enzymes in saliva) iii. Lined w nonkeratinized stratified squamous epithelium iv. Anatomical locations: 1. Bound anteriorly by teeth/lips; posteriorly by the oropharynx; superiorly by hard/soft palates; inferior surface formed by the mylohyoid muscle. Tongue attached to floor v. 2 regions:
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1. Vestibule —space b/w lips and gums 2. Oral cavity proper —lies central to the alveolar process of the mandible and maxillae B. Cheeks, Lips, Palate i. Cheeks—forms lateral walls of oral cavity 1. Covered externally by the integument 2. Contain buccinators muscles —hold cheeks against teeth to hold solids in place during chewing ii. Lips—forms anterior wall of oral cavity 1. Formed by orbicularis oris muscle 2. Keratinized stratified squamous epithelium 3. Red b/w lots of superficial blood vessels and reduced amt of keratin in outer epithelial layer. iii.
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