Secretion - THE DIGESTIVE SYSTEM Topic 3: Secretion...

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THE DIGESTIVE SYSTEM Topic 3: Secretion Graphics are used with permission of: Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com) Page 1: Title Page Digestive system secretion involves the production and release of juices and hormones by the GI tract and its accessory glands. Page 2: Goals To list the secretions of the digestive tract To describe the function of each secretion To describe the control of secretion throughout the digestive tract. Page 3: Large volumes of fluid move in and out of the GI tract For a typical daily consumption of food (800 g) and fluid (2.0 L): o About 1.5 L of saliva is secreted into the mouth. o About 2.0 L of gastric juice are produced o The pancreas delivers about 1.5 L of pancreatic juice to the duodenum o The liver/gallbladder delivers about 0.5 L of bile into the duodenum o The small intestine produces about 1.5 L of fluid o The total of all of the above secretions = about 9.0 L The small intestine absorbs about 8.5 L of fluids & most of the ingested food The large intestine absorbs about 0.35 L of fluid, some salts and vitamin K Although the GI tract contains about 9.0 L of fluid every day, only about 0.15 L is eliminated with the feces Of the approximately 800 g of food ingested in a typical daily diet, only about 50 g (< 10%) of undigested food are eliminated as feces Page 4: Salivary glands secrete saliva The extrinsic salivary glands include the paired parotid, submandibular and sublingual glands
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Parotid glands produce serous fluid containing enzymes, electrolytes, and limited mucin Submandibular and sublingual gland produce a more viscous fluid than parotid glands Saliva functions include: o Protection (esp. antibacterial lysozyme and IgA antibodies) o Taste (dissolved food chemicals) o Lubrication (mucus) o Digestion (esp. starch via amylase) Page 5: The esophagus secretes mucus The only secretion of the esophagus is mucus Page 6: Gastric secretions are produced regionally The gastric mucosa produces exocrine, endocrine, and paracrine secretions* Exocrine secretions, collectively called gastric juice, include mucus, pepsinogen, HCl, and intrinsic factor; they are released into the stomach lumen as follows: o Mucus – throughout the stomach o Pepsinogen – throughout the stomach o HCl – fundus and body o Intrinsic factor (IF) – fundus and body *Play the animation on page 6 of the Secretion topic to help reinforce this regional distribution of chemical secretions in the stomach.
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Enteroendocrine cells in the pylorus release gastrin into the bloodstream;
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Secretion - THE DIGESTIVE SYSTEM Topic 3: Secretion...

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