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PHGY210- Lecture 24- Dr. Wechsler.docx

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PHGY 210
Ann Wechsler

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thLecture 24 Friday March 5 2010PHYSIOLOGY OF THE GASTROINTESTINAL TRACT GITANDITS ACCESSORY STRUCTURESDr Ann WechslerRoom 1135 McIntyre5143984341annwechslermcgillcaGIT Role in Homeostasis Provide Nutients see slidesEarthworm Tubular structure of the earthworm GIT maintained in humans Communication with external environment also maintainedGrowth Enormous elongation of the tract from mouth to anus GIT is many times the length of the human body around 45 meters Surface area of the lining of the lumen of the GIT also increases Internal surface area is 600x the area of the outer lining 200250 m squaredDifferentiation Manifests into different regions of the tube specialized to perform specific aspects of digestion see slidesWall Structure Text pg 581 Four recognizable layers 1 Outer layer is the Serosa Tough layer continuous with the mesenteries lining the abdominal cavity 2Next layer towards the lumen is the Muscularis Externa which is 2 layers of muscle Outermost layer has fibres arranged parallel to the lengths of the digestive tube when they contract the tract will shorten Underneath are the circular fibres of muscle spiral arrangement wound around the circumference when they contract the lumen diamter decreases in size Aside atriated muscle up until esophagus rest smooth muscle 3 Next layer towards the lumen is a layer of loose connective tissue with lots of blood vessels and nerve fibres called the Submucosa 4 The innermost layer is the Mucosa thin layer of muscle smooth Muscylaris Mucosae and the Lamina Propria Innermost later is the epithelial layer and are composed of endocrine and exocrine cells More detail 1Serosathin tough layer of connective tissue continuous in places with abdominal mesentery 2Muscularis Externaouter layer longitudinal fibres when it contracts GIT shortens inner layer circular fibres when it contracts lumen narrows musculature in oral cavity pharynx upper 13 esophagus and external anal sphincter is striated the rest is smooth
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