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Digestive System Part I

Digestive System Part I - Digestive System The organs that...

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Digestive System The organs that are involved in the breaking down of food into molecules that can pass through the wall of the digestive tract and can be taken up by the cells. Digestive Processes There are five basic activities that are involved in the digestive process 1. Ingestion - The taking of food into the mouth. 2. Mixing and movement of food - Involves the muscular contractions (paristalsis) that mix the food and move it along the digestive tract. 3 . Digestion - The break down of food by mechanical and chemical means. 4. Absorption - The passage of food from the digestive tract into the cardiovascular and lymphatic system. 5. Defecation - The elimination of indigestible waste. Digestion: Two Stages Mechanical digestion Physical breakdown of food into smaller particles by the cutting and grinding action of the teeth and the churning contractions of the stomach and small intestines Serves to expose more food surface to the actions of the digestive enzymes Digestion: Two Stages Chemical digestion A series of hydrolysis reactions that break macromolecules into their monomers Polysaccharides into monosacharides Proteins into amino acids Nucleic acids into nucliotides Fats inito glycerol and fatty acids Hydrolysis carried out by digestive enzymes from the Salivary glands, stomach Pancreas small intestine Some foods are absorbed without enzymatic action Vitamins, free amino acids, minerals, cholesterol, and water Processes in Digestion Motility - the muscular contractions that break up food, mix, and propel food Secretion - the release of enzymes and hormones that carry out and regulate digestion Membrane transport- all the mechanisms that absorb nutrients and transfer them into the blood and lymph (active transport, facilitated diffusion, etc.) Organization GI tract or Alimentary canal - the continuous tube that begins at the mouth and ends at the anus. Mouth, pharynx, esophagus, stomach, small intestine, and large intestine Accessory organs- Aid in the digestive process by mechanical manipulation and secreting various substances (enzymes, mucus) teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
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Four Layers of the GI Tract Mucosa Epithelium Lamina propria Muscularis muscosa Submucosa Muscularis Internal oblique (only in the stomach) Inner circular layer Outer longitudinal layer Serosa Areolar tissue mesothelium General Histology Mucosa The inner layer of the tract that is a mucous membrane that is composed of a layer of epithelium- simple columnar in most of the GI tract Nonkeratinized stratified squamous from the oral cavity through the esophagus and in the lower anal canal (areas subject to abrasion) Lamina propria- areolar connective tissue containg blood and lymphatic vessels muscularis mucosae- a thin layer of smooth muscle ( is responsible for the mucosal folds, or rugae , that serves to increase the surface area for digestion. Is the most highly differentiated layer of the GI tract.
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Digestive System Part I - Digestive System The organs that...

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