Picture plates - PLATE 21 Organization and Functions of the...

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PLATE 21: Organization and Functions of the Digestive System The digestive system functions to ingest, digest and absorb food substances into the blood stream and to eliminate remaining wastes. The digestive structures in the mouth and stomach act primarily in the mechanical and chemical digestion of food. The Small Intestine acts in chemical digestion of food substances and absorption of resultant nutrients. The Large Intestine (colon) absorbs remaining water and salts and excretes waste products of digestion (feces) through its exit end, the rectum and anus. To facilitate digestion, numerous exocrine glands secrete a variety of alkaline or acidic juices containing enzymes and mucus into the digestive lumen. The large and separately located pancreas, liver, and salivary glands constitute the accessory digestive glands. The numerous small stomach and intestinal glands form an instrinsic part of the gut wall. During the absorption process the breakdown, the breakdown products of proteins, carbohydrates, nucleic acids, water, minerals, and water-soluble vitamins, are transported across the intestinal mucosa into the hepatic portal circulation for delivery to liver and bloodstream. Fats and fat-soluble vitamins, however, are absorbed via the lacteals and lymph vessels for delivery to the blood via the lymphatic circulation. Dietary foods are rarely found in a readily absorbable form. They facilitate digestion but are not absorbed. Complex Dietary Substances= Proteins Carbohydrates and Fats Digestive enzymes secreted by the pancreas and other digestive glands hydrolyze complex dietary substances into simpler and small molecules that can be readily absorbed by the intestinal mucosa into the bloodstream. PLATE 72: Digestion in the Mouth: Chewing, Saliva, and Swallowing Mechanical Events: The chewing action (mastication) carried out by the mouth and its associated structures (lips tongue, cheeks, teeth, jaw) mechanically breaks the food materials into smaller pieces and forms a bolus for swallowing In the adult human, a total of 32 permanent teeth break up food materials.
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