CHAPTER 26 Summary
In-Class Activity
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The digestive system is composed of a central digestive tract and accessory organs. Its function is to break down food molecules into smaller subunits, absorb nutrients, and eliminate waste.-
Digestion begins in the mouth, where teeth chew food (mechanical digestion) and salivary enzymes begin breaking down carbohydrates (chemical digestion).
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Food passes from the mouth into the stomach through the esophagus, propelled by waves of muscular contractions called peristalsis.
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The stomach is muscular and acidic and contains a protein-digesting enzyme called pepsin. It is elastic and can expand after a large meal to store food for a few hours.
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Food processed in the stomach is called chyme. Chyme passes into the small intestine, where enzymes further digest it.
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Bariatric surgery reduces the size of the stomach so that it can no longer hold as much food. The surgery may also shorten the small intestine. As a result, fewer Calories are taken in and absorbed, and weight loss occurs.
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Enzymes from the pancreas help to digest organic molecules in the small intestine.
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Bile salts, produced in the liver and stored in the gallbladder, emulsify fats and help the body digest them.
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Epithelial cells that line the small intestine absorb the broken-down products of food; once absorbed, food molecules enter the bloodstream and are transported throughout the body.
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The large intestine absorbs water and forms solid stool from indigestible matter in food such as fiber.
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Humans and many other animals have a complete digestive tract—one with a mouth and an anus. Not all organisms have a complete digestive tract; many have no digestive tract at all.
MORE TO EXPLORE
Centers for Disease Control and Prevention: Obesity http://www.cdc.gov/obesity/
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Mingrone, G., et al. (2012) Bariatric surgery versus conventional medical therapy for type 2 Diabetes. New England Journal of Medicine 366(17):1577–1585.
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Sjöström L., et al. (2007) Effects of bariatric surgery on mortality in Swedish obese subjects. New England Journal of Medicine 357:741–752.
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Nestle, M., and Malden, N. (2012) Why Calories Count: From Science to Politics. Berkeley: University of California Press.
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Brownell, K., and Horgen, K. B. (2004) Food Fight: The Inside Story of The Food Industry, America’s Obesity Crisis, and What We Can Do About It. New York: McGraw-Hill.
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