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PSL201 – March 20 GI 1 & 2.docx

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Michelle French

PSL201 – March 20 – GI 1 & 2 Generalized Structure of the Gastrointestinal Wall 4 distinct layers: - mucosa: lines the lumen of the digestive tract - submucosa: underlying layer of connective tissue - muscularis externa: layer made up of primarily smooth muscle fibers - serosa (adventitia): outter layer composed of mostly connective tissue Mouth, Pharynx, and Esophagus - mouth is the beginning of the GI tract o chewing = mastication - saliva: lubricates food and secretes an enzyme (salivary amylase) which begins deigestion by breaking down starch and glycogen - from there food is propelled by the tongue into the pharynx (throat) - then to the esophagus o a muscular tube that conducts food from the pharynx to the stomach o thin-walled and pliant to accommodate food (collapsed in absence of food) o circular muscles contract behind food and relax infront of it as it passes down the esophagus The Stomach - j-shaped sac located beneath the diaphragm - stores food after it is digested and stores until released into the small intestine - lining of glands in stomach (gastric glands) that secrete a watery gastric juice into the lumen - contractile action pulverizes food into smaller pieces and mixes it with juices, producing chyme - 3 anatomical regions: o domed upper fundus (wall is thin and easily expands) o middle body o lower antrum contracts push chime into intestine - chime passes through a narrow passage (pylorus) on the way to the SI o regulated by the pyloric sphinter which opens and closes w/ each cycle of stomach contractions - gastric pits – secrete products found in gastric juice o neck cells: upper part of the pits  secret
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