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6.1 / D.2

digestion &  absorption

"IT ALL COMES DOWN TO POO"

Essential Ideas:  The structure of the wall of the small intestine allows it to move, digest, and absorb food.  Digestion is controlled by nervous and hormonal mechanisms.

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Nature of Science: Use models as representations of the real world: dialysis tubing can be used to model absorption in the intestine.  Serendipity and scientific discoveries:  the role of gastric acid in digestion was established by William Beaumont while observing the process of digestion in an open wound caused by gunshot.

UNDERSTANDINGS:

  • 6.1.U1  The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut.

  • 6.1.U2  The pancreas secretes enzymes into the lumen of the small intestine.

  • 6.1.U3  Enzymes digest most macromolecules in food into monomers in the small intestine.

  • 6.1.U4  Villi increase the surface area of epithelium over which absorption is carried out.

  • 6.1.U5  Villi absorb monomers formed by digestion as well as mineral ions and vitamins.

  • 6.1.U6  Different methods of membrane transport are required to absorb different nutrients.

  • D.2.U1  Nervous and hormonal mechanisms control the secretion of digestive tissues.

  • D.2.U2  Exocrine glands secrete to the surface of the body or the lumen of the gut.

  • D.2.U3  The volume and content of gastric secretions are controlled by nervous and hormonal mechanisms.

  • D.2.U4  Acid conditions in the stomach favor some hydrolysis reactions and help control pathogens in ingested food.

  • D.2.U5  The structure of cells of the epithelium of the villi is adapted to the absorption of food.

  • D.2.U6  The rate of transit of materials through the large intestine is positively correlated with their fiber content.

  • D.2.U7  Materials not absorbed are egested.

APPLICATIONS & SKILLS:

  • Application:  Processes occurring in the small intestine that result in the digestion of starch and transport of products of digestion to the liver.

  • Application:  Use of dialysis tubing to model absorption of digested food in the intestine.

  • Skill:  Production of an annotated diagram of the digestive system.

  • Skill:  Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph.

  • Application:  The reduction of stomach acid secretion by proton pump inhibitor drugs.

  • Application:  Dehydration due to cholera toxin.

  • Application:  Helicobacter pylori infection as a cause of stomach ulcers.

  • Skill:  Identification of exocrine glands that secrete digestive juices and villus epithelium cells that absorb digested foods from electron micrographs.

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RESOURCES:

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