Gastrointestinal_System_Chapter_20 -...

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Gastrointestinal System Chapter 20 The main function of the digestive system is to transfer nutrients, water, and electrolytes from ingested food into body’s internal environment. 4 functions : Motility : muscular contractions that mix an move the contents forward of the digestive tract Secretion: transfer of digestive juices by exocrine glands into the digestive tract Digestion: chemical change (hydrolysis) of large molecules (e.g., carbohydrates, proteins, and fats) into their smaller subunits (e.g. starch in glucose, proteins into amino acids, etc.) Absorption: passage of the products of digestion (e.g., glucose), along with water, vitamins, and electrolytes, into the blood and lymph Structures of the Gastrointestinal Tract Mouth, pharynx, and esophagus Stomach Small intestine Colon Rectum and anus Layers of GI Tract Mesentery : holds organs in place Mucosa Lines the lumen contains lymph nodes gets rid of invaders that may have come in with food Goblet cells : Secrete mucus Motility Functions of the GI Tract Movement of food through the GI tract. Ingestion : Taking food into the mouth Mastication : chewing the food and mixing it with salvia Deglutition : swallowing the food Peristalsis : Rhythmic wave-like contractions that move food through GI tract. The oral cavity Mastication by the teeth is the first step grinds and breaks the food into smaller pieces. mixes food with Enzyme : salivary amylase chemically changes starch . Lysozyme in the saliva lyses bacteria. Saliva also keeps the mouth and teeth clean. Salivary secretion is continuous Salivary Glands
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Saliva Bicarbonate Mucus Salivary amylase Lysozyme Esophagus Muscular tube from pharynx to stomach Upper 1/3 – skeletal muscle Lower 2/3 – smooth muscle Upper esophageal sphincter Skeletal muscle Between pharynx and esophagus Lower esophageal sphincter or cardia spinchter Smooth muscle Between esophagus and stomach Swallowing Refles Bolu descends in pharynx, pressing on epiglottis Epiglottis covers glottis so food does not enter traches Inhalation is ihibited Bolus arrives at stomach Triggers relaxation of cardiac sphincter Bolus enters stomach Stomach Stored food after swallowed Emopty = 50 mL Full = 1000 mL Secretes gastric juice The mixing movements of the antrum produces chyme Releases food as chyme into intestine slowly The stomach stores food and begins protein digestion. Its terminal part has a pyloric sphincter The most important function of the stomach is to store food. Parietal cells secrete HCl
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This note was uploaded on 05/12/2011 for the course BIOL 2160 taught by Professor Kt during the Fall '08 term at LSU.

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Gastrointestinal_System_Chapter_20 -...

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