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1104 chapter 15 Digestive System

1104 chapter 15 Digestive System - 1104 chapter 15...

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1104 chapter 15 Digestive System The digestive system consists of a long, hollow tube, called the GI (gastrointestinal tract , into which various accessory glands release their secretions. The hollow area of the tube that food and fluids travel through is called the lumen. Most of the GI tract have 4 basic layers. 1. Mucosa : The innermost layer is the moist, mucus-secreting layer called the mucosa. The mucus helps lubricate the tube allowing food to slide through easily. Mucus also helps protect the cells in the lining from rough substances in the food and from digestive enzymes. 2. Submucosa: the next layer, the submucosa, consists of connective tissue containing blood vessels, lymph vessels, and nerves. The blood supply maintains the cells of the digestive system and in some regions pick up and transport the products of digestion. The nerves are important in coordinating the contractions of the next layer 3. Musculairs: The next layer, the muscularis, is responsible for movement of materials along the GI tract and for mixing materials with digestive secretions. It is a double layer of smooth muscles. (circular and longitudinal muscle). The muscle layers churn the food until it is liquefied, mix the resulting liquid with enzymes, and propel the food along the GI tract is a process called peristalsis. 4. Serosa: A thin layer of epithelial tissue supported by connective tissue. There are two types of digestion : Mechanical digestion: the physical breaking of food into smaller pieces; and another is chemical digestion , the breaking of chemical bonds so that complex molecules are taken apart into smaller subunits 1. Mouth: Mouth receives the food and prepares it for swallowing in the oral cavity. 2. There are receptors called taste buds present on the tongue that determine the taste of food 3. the roof of mouth separates the oral cavity from the nasal cavity. The roof has two parts, anterior hard palate and a posterior soft palate. The soft palate ends into a projection called uvula. The tonsils present on both sides of oral cavity play a role in protecting the body from disease causing organisms.
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