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Digestion Powered By Docstoc
   Digestion is the process of breaking
    down foods into nutrients to prepare for
    absorption while overcoming 7
   Anatomy of the Digestive Tract –
    The gastrointestinal (GI) tract is
    the flexible muscular tube from
    mouth to anus. The lumen is the
    inner space of the tract.
The start of the process –
the mouth:
   The digestive process begins in the
    mouth. Food is partly broken down by
    the process of chewing (mastication)
    and by the chemical action of salivary
    enzymes (amylase) These enzymes are
    produces by the salivary glands and
    break down starches into smaller
On the way to the stomach:
the esophagus
   After being chewed and swallowed, the
    food enters the esophagus. The
    esophagus is a long tube that runs from
    the mouth to the stomach. It uses
    rhythmic, wave-like muscle movements
    (called peristalsis) to force food from
    the throat into the stomach. This
    muscle movement gives us the ability to
    eat or drink even when we're upside-
In the stomach -
   The stomach is a large, sack-like
    organ that churns the food and
    bathes it in a very strong acid (gastric

   Food in the stomach that is partly
    digested and mixed with stomach
    acids is called chyme
In the small intestine
   After being in the stomach, food enters the
    duodenum, the first part of the small
   It then enters the jejunum and then the
    ileum (the final part of the small intestine).
   In the small intestine, bile (produced in the
    liver and stored in the gall bladder),
    pancreatic enzymes, and other digestive
    enzymes produced by the inner wall of the
    small intestine help in the breakdown of food.
In the large intestine
   After passing through the small intestine,
    food passes into the large intestine. In
    the large intestine, some of the water
    and electrolytes (chemicals like sodium)
    are removed from the food.
   Many microbes (bacteria like
    Bacteroides, Lactobacillus acidophilus,
    Escherichia coli, and Klebsiella) in the
    large intestine help in the digestion
In the large intestine
   The first part of the large intestine is
    called the cecum (the appendix is
    connected to the cecum).
   Food then travels upward in the
    ascending colon. The food travels
    across the abdomen in the transverse
    colon, goes back down the other side of
    the body in the descending colon, and
    then through the sigmoid colon.
     The end of the process
   Solid waste is then
    stored in the rectum
    until it is excreted via
    the anus.
   The Secretions of Digestion
      Includes digestive enzymes that act as
       catalysts in hydrolysis reactions
       Saliva from the salivary glands moistens foods
       Gastric juice from the gastric glands includes
        hydrochloric acid. The goblet cells of the
        stomach wall secrete mucus to protect the
        walls of the stomach from the high acidity
        levels that are measured by pH units.
   The Secretions of Digestion
      Pancreatic juice contains intestinal
       enzymes (carbohydrase, lipase, protease)
       and bicarbonate.
       Bile is produced by the liver, stored in the
        gall bladder, and acts as an emulsifier to
        suspend fat.
   The Final Stage
       Energy-yielding nutrients are disassembled
        for absorption.
       Vitamins, minerals and water can be
       Undigested residues, including some fibers,
        continue through the digestive tract and
        form stool.
       Recycling of usable materials
   The enormous surface area of the small
    intestine facilitates nutrient absorption.
   Nutrients can be absorbed through
    simple diffusion, facilitated diffusion, or
    active transport.
   Outside                                      Carrier loads               Carrier loads
   cell                                         nutrient on                 nutrient on
                                                outside of cell . . .       outside of cell . . .

Inside                                                . . . and then                . . . and then
cell                                                  releases it on               releases it on
                                                      inside of cell.              inside of cell.
           SIMPLE                      FACILITATED                          ACTIVE
          DIFFUSION                     DIFFUSION                         TRANSPORT

 Some nutrients (such      Some nutrients (such as the water-      Some nutrients (such as
 as water and small        soluble vitamins) are absorbed by       glucose and amino acids)
 lipids) are absorbed by   facilitated diffusion. They need a      must be absorbed actively.
 simple diffusion. They    specific carrier to transport them      These nutrients move
 cross into intestinal     from one side of the cell membrane      against a concentration
 cells freely.             to the other. (Alternatively,           gradient, which requires
                           facilitated diffusion may occur         energy.
                           when the carrier changes the cell
                           membrane in such a way that the
                           nutrients can pass through.)                               Stepped Art
                                                                                    Fig. 3-9, p. 81
   Anatomy of the Absorptive System
       Villi are the fingerlike projections within the folds
        of the small intestine that move in a wave-like
        pattern to trap nutrients.
       Microvilli are the microscopic hairlike projections
        on each villi.
       Crypts are the tubular glands that lie between the
        intestinal villi.
       Goblet cells are located between the villi and
        secrete a protective thick mucus.
   A Closer Look at the Intestinal Cells
       Specialization of the cells to absorb different nutrients
       “Food combining” which emphasizes separating food
        for digestive purposes is a myth.
       Preparing Nutrients for Transport
          Water-soluble nutrients and small products of fat

           digestion are released to the bloodstream.
          Fat-soluble vitamins and larger fats form

           chylomicrons and are released to the lymphatic
Common Digestive Problems
   Food becomes lodged in the trachea.
   The larnyx cannot make sounds.
   The Heimlich maneuver may need to be used.
   Strategies
       Small bites
       Chew thoroughly.
       Don’t talk or laugh with food in the mouth.
       Don’t eat when breathing hard.
   Body’s adaptive mechanism
   Dehydration is a concern.
   May be self-induced as in eating
   Frequent, loose, watery stools
   Irritable bowel syndrome or colitis is
    one of the common GI disorders.
   Strategies
       Rest
       Drink fluids
       Medical help is needed if it persists.
Thought of the day

       Never, under any
     circumstances, take a
       sleeping pill and a
           laxative on
         the same night
   Defecation habits are different among people.
   Many causes are possible.
   Hemorrhoids may be a problem.
   Diverticulosis is a condition in which the
    intestinal walls weaken and bulge. The
    bulging pockets are called diverticula.
    Diverticulitis is a worsened condition and
    requires intervention.
   Use of laxatives, enemas and mineral oil may
    not be necessary with lifestyle changes.
   Colonic irrigation is the internal washing of
    the large intestine and can be hazardous.
   Strategies
       High-fiber diet
       Increased fluids
       Exercise regularly.
       Respond quickly to the urge to defecate.
Belching and Gas
   Strategies
       Eat slowly.
       Chew thoroughly.
       Relax while eating.
       Watch bothersome foods.
   Hiccups are triggered by eating or
    drinking too fast.
Heartburn and
“Acid Indigestion”
   Gastroesophageal reflux is the
    backward flow of stomach contents into
    the esophagus.
   Antacids and acid controllers may help
Heartburn and
“Acid Indigestion”
   Strategies
       Small meals
       Liquids between meals
       Sit up while eating.
       Wait 1 hour after eating before lying down.
       Wait 2 hours after eating before exercising.
       Refrain from tight-fitting clothing.
       Avoid bothersome foods.
       Refrain from tobacco use.
       Lose weight if overweight.
   Peptic ulcers can be gastric or
   Strategies
       Take prescribed medicine.
       Avoid caffeine- and alcohol-containing
       Minimize aspirin and ibuprofen use.
       No smoking.

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