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Medical Where does digestion begin?

  1. Jan 23, 2012 #1
    Most textbooks say it begins in the mouth. In fact, THAT is a quote from a text. Does it? Define digestion, specifically. So where does it begin?
  2. jcsd
  3. Jan 23, 2012 #2


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    Staff: Mentor

    In the mouth. Saliva starts the digestive process.


    What, specifically, do you not understand?
  4. Jan 23, 2012 #3


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    What do you define as digestion? Does it begin with breaking the food before you eat it, mastication in your mouth or any place farther on the line. Personally, I'd start with mastication as a beginning point. There's a lot of other stuff going on in your mouth though. Take a bite of a Saltine cracker. You get the salty taste, and the initial crisp of the crust, and then that starch starts getting sweet. Some folks don't learn to appreciate their food (and the way their body processes it), but the progression of food ingredient flavors (not as simple as Saltines most of the time) can be important to complex dishes. (Ed.) I'm not one of the "chew every mouthful 40 times" nuts, but there is a good argument for savoring your meals.
  5. Jan 23, 2012 #4


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    Mastication certainly counts. But even without it, saliva is full of enzymes that begin the chemical breakdown.
  6. Jan 23, 2012 #5


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    In the frying pan
  7. Jan 23, 2012 #6


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    2017 Award

    If we define digestion as "the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream" (definition from Wikipedia), then I would agree with Pythagorean that cooking can be counted as an important step in digestion. Cooking mechanically and chemically modifies foods such that the nutrients are much easier for our digestive systems to absorb. Heat, for example, aids to denature tough proteins in meats like collagen, making these foods easier to digest and break down into amino acids. For example, one study showed that humans are capable of absorbing only 51-65% of the protein content in raw eggs, but when the eggs are cooked, humans can absorb 91-94% of the proteins. Some anthropologists have even suggested that the invention of fire and cooking was a key step in human evolution. A species that consumes a diet of cooked foods would not require as many resources to be spent on its digestive system as cooked foods take less effort to digest than raw foods. Furthermore, a diet of cooked foods would provide that species with much more energy. Therefore, such a species could devote more of its resources and energy to the function of other organs, such as the brain.

    Of course, the textbook answer is that digestion begins in the mouth due to enzymes like salivary amylase which begin to chemically digest food.
  8. Jan 24, 2012 #7
    I was also taught that digestion starts in the mouth. The teeth mechanically separate food and break it down into smaller pieces.
  9. Jan 25, 2012 #8


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    My father's mother was a professional cook (for a logging/river-driving company) for many years. She hated to see any of us grand-kids hogging down our food. When I was a kid, she'd try to kidnap me for a week or two every summer (because she thought I was too skinny) and she'd blur the gaps between meals and keep me eating on and off all day long. She put 10# on my skinny frame in two weeks once, but I ran it off in no time. Good eats, though!
  10. Jan 25, 2012 #9
    I think it might begin somewhere in the sensory system and when the prospect of food becoming available triggers the production of extra saliva.
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