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The Four Stages of Digestion
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The process in which food is broken
down, nutrients are absorbed, and
wastes eliminated is called digestion
and occurs in the digestive system.
The fours stages of digestion are:
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Ingesting
Digesting
Absorbing
Eliminating
See page 70
(c) McGraw Hill Ryerson 2007
Stage 1: Ingesting
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Ingesting, or ingestion, means
to bring food into the body. This
is the starting point of the
digestive process.
See page 71
(c) McGraw Hill Ryerson 2007
Stage 2: Digesting
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The Mouth
Mechanical digestion occurs when
your teeth and tongue break food
into small enough pieces to swallow.
Each small piece of food is called
bolus.
Chemical digestion occurs when
saliva begins to break down the
bolus.
An enzyme in your saliva (amylase)
begins to break down simple and
complex carbohydrates.
See page 71
(c) McGraw Hill Ryerson 2007
Stage 2: Digesting
The Esophagus
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When you swallow, your food
enters the esophagus.
The esophagus is a long
muscular tube that carries
food to your stomach.
The bolus is pushed through
the esophagus in a process
called peristalsis.
See page 72
(c) McGraw Hill Ryerson 2007
Stage 2: Digesting
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The Stomach
Inside the stomach is gastric
juice, which is very acidic.
(Hydrochloric acid)
The stomach walls are lined with
mucus to protect the tissue from
being damaged by the acid.
An enzyme called pepsin, present
in gastric juice, works with the
acid to, break down protein
The bolus that enters your
stomach breaks down into a liquid
called chyme.
See page 73
(c) McGraw Hill Ryerson 2007
Stage 2: Digesting
The Small Intestine
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The first meter of the small
intestine is called the
duodenum.
The pancreas adds enzymes
that help break down the
carbohydrates, protein, and fat
in the chyme.
The liver produces bile which is
stored in the gall bladder.
Bile breaks the globs of fat into
smaller droplets.
See page 74
(c) McGraw Hill Ryerson 2007
Stage 3: Absorbing
The Small and Large Intestine
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Absorption is the process in
which nutrients and water are
absorbed by the small and
large intestine.
The small intestine is covered
with villi to help increase the
rate at which nutrients are
absorbed.
The large intestine absorbs
water and some minerals.
See page 75
(c) McGraw Hill Ryerson 2007
Stage 4: Eliminating
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Any solid material, undigested by
the end of the large intestine is
called feces.
Feces are stored in the rectum
until they are eliminated through
the anus.
Liquid and gas wastes are
removed by your excretory
system.
 The main organs in your excretory
system are your kidneys and your
bladder.
See page 76
(c) McGraw Hill Ryerson 2007
Eating Disorders
• Anorexia nervosa is a
disorder when a person
severely restricts what
they eat.
• Bulimia nervosa is a
disorder when a person
eats large amounts of
food and then vomits or
takes laxatives to get rid
of the food before it is
completely digested.
Take the Section 2.2 Quiz
See page 77
(c) McGraw Hill Ryerson 2007