ireland3e_digestion_ch15_fall11

ireland3e_digestion_ch15_fall11 - 10/26/2011 Chapter 15 The...

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10/26/2011 1 Chapter 15 The Digestive System The Digestive System The digestive system has two major parts the gastrointestinal system or GI tract the GI tract begins at the oral cavity, winds through the abdominal cavity, and ends at the anus a set of accessory organs the major accessory organs include the pancreas, the liver, and the gallbladder Together the GI tract and the accessory organs carry out five basic processes: ingestion - foods and liquids are taken into the mouth and eaten mixing - the smooth muscle in the walls of the GI tract mixes the food and sends it on its way through the tract digestion - food is broken down by both mechanical and chemical processes absorption - the epithelial cells lining the GI tract absorb the digested food molecules and pass them to the blood or lymph defecation - any substance not digested or absorbed, for whatever reason, is passed along to the end of GI tract, the anus, and leaves the body
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10/26/2011 2 The Digestive System The GI Tract The structure of the GI tract is essentially the same along its entire length It is composed of four layers: the innermost layer is composed of a mucous membrane, or mucosa it is a slippery, smooth layer which allows ingested food to move along the tract without tearing it under the mucosa, the submucosa includes the glands, nerves, and blood supply for the tract itself the muscularis gives the tract the ability to move substances lengthwise it is (mostly) composed of one layer of longitudinal muscle above another layer of circular muscle the outer layer of the GI tract, the serosa , is a slippery membrane that permits the tract to move inside the abdominal cavity without catching or causing discomfort These layers work in unison to create the peristaltic wave that propels food through the tube
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10/26/2011 3 The GI Tract The GI Tract
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10/26/2011 4 Mechanical Digestion Mechanical Digestion teeth function as cutting tools (incisors), piercing and ripping utensils (canines), or grinding instruments (molars and premolars) small bits of food are macerated with saliva Mechanical digestion increases the efficiency of enzymes in the stomach and small intestine by creating small bits of food with a great deal of surface area where enzymes can carry out the process of chemical digestion MALT Food is rarely sterile, and yet we almost never suffer disease from ingesting it Starting with the tonsils, the mucosa of the GI tract contains a disease- prevention tissue called MALT (mucosa-associated lymphatic tissue) MALT is also prevalent in the small intestine, large intestine, and appendix These nodules of lymphatic tissue prevent pathogens from taking over the lumen of the digestive tract and are important for preserving homeostasis MALT tissues represent a large percentage of the entire immune system, including about half of the body's total lymphocytes and macrophages without MALT, pathogens could grow within the digestive tract, penetrate the epithelial lining, and cause serious internal infections
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This note was uploaded on 12/26/2011 for the course BSC 2023 taught by Professor Staff during the Fall '08 term at FIU.

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ireland3e_digestion_ch15_fall11 - 10/26/2011 Chapter 15 The...

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