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Small Intestine

Small Intestine . Pgs. 921-927 (not including absorption) . Small Intestine – Basics . Majority of digestion and absorption takes place large surface area for both activities (enhanced by circular folds, microvilli , and villi Starts at pyloric sphincter and opens to large intestine

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Small Intestine

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  1. Small Intestine Pgs. 921-927 (not including absorption)

  2. Small Intestine – Basics • Majority of digestion and absorption takes place • large surface area for both activities (enhanced by circular folds, microvilli, and villi • Starts at pyloric sphincter and opens to large intestine • Avg. length = 10 ft. / 2.5 cm in diameter

  3. Small Intestine Anatomy 3 main regions: 1. duodenum 2. jejunum – about 1 meter 3. illeum – longest portion; about 2 meters - joins large intestine at ileocecal sphincter

  4. Small Intestine – Histology • Epithelial layer: composed of simple columnar - many different types of columnar cells (functions)

  5. Types of Epithelial Cells Absorptive cells – digest and absorb nutrients from chyme Goblet cells – secrete mucus Paneth cells – secrete lysozyme; capable of phagocytosis

  6. Small Intestine – Histology Muscularis = smooth muscle Circular folds = increase surface area for absorption and cause chyme to spiral Villi = also increase surface area Microvilli = composed of actin filaments; increase surface area; too small to be seen by light microscope (brush border) – secrete enzymes

  7. Intestinal Juice and Brush-Border Enzymes • Composed of water and mucus (pH = 7.6) • Along with pancreatic juice provides a liquid medium for absorption of nutrients from chyme • Absorptive cells secrete many enzymes and secrete them to the membrane of the microvilli (brush-border enzymes) - carb digesting enzymes (maltase, sucrase, lactase) - protein digesting enzymes – peptidases - nucleotide digesting enzymes – nucleosidases & phosphatases

  8. Mechanical Digestion • 2 types of movements 1. segmentation – mix chyme with digestive juices; bring mixture into contact with mucosa for absorption (no movement) 2. after absoption has stopped, peristalsis begins – movement of material through the small intestine

  9. Chemical Digestion • Chyme entering small intestine contains partially digested carbs. (salivary amylase), proteins, and lipids • To complete digestion – combination of pancreatic juice, bile, and intestinal juice

  10. Enzymes Alpha-dextrinase Sucrase Lactase Maltase Aminopeptidase Dipeptidase Nucleosidases Phosphatases

  11. Other Information for Final • Large intestine • Phases of Digestion (937 – 939) • What will not be on exam: 1. Absorption in small intestine 2. Peritoneum (900 – 902)

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