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Unformatted text preview: Introduction to the Digestive System Acquires nutrients from environment Anabolism Uses raw materials to synthesize essential compounds Catabolism Decomposes substances to provide energy cells need to function Catabolic Reactions Require two essential ingredients: 1. Oxygen 2. Organic molecules broken down by intracellular enzymes: – e.g., carbohydrates, fats, and proteins Digestive Tract Digestive tract also called gastrointestinal (GI) tract or alimentary canal Is a muscular tube Extends from oral cavity to anus Passes through pharynx, esophagus, stomach, and small and large intestines Functions of the Digestive System 1. Ingestion : Occurs when materials enter digestive tract via the mouth 2. Mechanical processing : Crushing and shearing Makes materials easier to propel along digestive tract 3. Digestion : The chemical breakdown of food into small organic fragments for absorption by digestive epithelium 4. Secretion : Is the release of water, acids, enzymes, buffers, and salts By epithelium of digestive tract By glandular organs 5. Absorption : Movement of organic substrates, electrolytes, vitamins, and water Across digestive epithelium Into interstitial fluid of digestive tract 6. Excretion : Removal of waste products from body fluids Lining of the digestive tract protects surrounding tissues against Corrosive effects of digestive acids and enzymes Mechanical stresses, such as abrasion Bacteria either ingested with food or that reside in digestive tract The Digestive Organs and the Peritoneum Lined with serous membrane consisting of Superficial mesothelium covering a layer of areolar tissue Serosa, or visceral peritoneum: – covers organs within peritoneal cavity Parietal peritoneum: – lines inner surfaces of body wall Peritoneal Fluid Is produced by serous membrane lining Provides essential lubrication Separates parietal and visceral surfaces Allows sliding without friction or irritation Mesenteries Are double sheets of peritoneal membrane Suspend portions of digestive tract within peritoneal cavity by sheets of serous membrane That connect parietal peritoneum With visceral peritoneum Areolar tissue between mesothelial surfaces Provides an access route to and from the digestive tract For passage of blood vessels, nerves, and lymphatic vessels Stabilize positions of attached organs Prevent intestines from becoming entangled Mesentery Development During embryonic development Digestive tract and accessory organs are suspended in peritoneal cavity by: – dorsal mesentery – ventral mesentery » later disappears along most of digestive tract except at the lesser omentum and at the falciform ligament The Lesser Omentum Stabilizes position of stomach Provides access route for blood vessels and other structures entering or leaving liver...
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