Transcript 9.4 Digestion in the Mouth and Stomach

Animal Anatomy & Physiology
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The digestive system
is used for breaking
down food into
nutrients which then
pass into the
circulatory system
and are taken to
where they are
needed in the body.
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4 main steps in digestion:
 Ingestion - the taking in of nutrients
 Digestion - the physical and chemical breakdown
of complex food molecules into smaller molecules
 Absorption - (the transfer of digested nutrients
from the digestive system to the bloodstream
 Egestion - the removal of waste food materials
from the body
Some simple animals,
such as flatworms or
jellyfish, have a
digestive sac with a
single opening into a
gastrovascular cavity.
 Nutrients are absorbed
by cells lining the cavity
and diffuse into all
other cells
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The human digestive system is
also a complete digestive
system. Unlike that of the
earthworm, the digestive tract
of humans is much longer than
the body

Often referred to as the
gastrointestinal tract (GI tract),
the human digestive tract is
approximately 7 m to 9 m long,
depending on the age and size
of the individual.
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Begins when food enters
the mouth.
It is physically broken
down by the teeth.
It is begun to be
chemically broken down
by amylase, an enzyme in
saliva that breaks down
carbohydrates.
The myth of the
tongue map;
that
1 tastes bitter,
2 tastes sour,
3 tastes salt,
and
4 tastes sweet.

In humans, digestion begins in
the mouth. Food is broken
down into smaller pieces by
the teeth (physical digestion).
Enzymes, like amylase begin
chemical digestion in the
mouth

Flat for grinding and crushing
food

Sharp for grabbing and
cutting food
HERBIVORE
CARNIVORE
The tongue moves
the food around until
it forms a ball called a
bolus.
 The bolus is passed to
the pharynx (throat)
and the epiglottis
makes sure the bolus
passes into the
esophagus and not
down the windpipe!
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http://www.youtube.com/watch?v=pNcV6yAfq-g
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The food stretches the
walls of the esophagus,
activating the smooth
muscles to undergo
rhythmic, wave-like
contractions called
peristalsis

sphincter the circular
muscle that
contracts to close an
opening in the body
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The stomach has folds called
rugae and is a big muscular
pouch which churns the bolus
(Physical Digestion) and mixes
it with gastric juice, a mixture
of stomach acid, mucus and
enzymes.
The acid kills off any invading
bacteria or viruses.
The enzymes help break down
proteins and lipids. Chemical
Digestion.
The mucus protects the lining
of the stomach from being
eaten away by the acid.
The stomach does do
some absorption too.
 Some medicines (i.e.
aspirin), water and
alcohol are all absorbed
through the stomach.
 The digested bolus is
now called chyme and it
leaves the stomach by
passing through the
pyloric sphincter.

S.I. is where most
digestion and absorption
of nutrients takes place
 S.I. is a tube only about
2.5cm in diameter but can
be 7m long.
 Made up of three
sections: the duodenum,
the jejunum, and the
ileum
 absorbed in the ileum
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Within each villus is
a network of tiny
blood vessels called
capillaries. All
nutrients, except
digested fats, enter
the bloodstream
through the
capillaries.
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The large intestine is
approximately 1.5 m in
length but is two to three
times larger in diameter
than the small intestine,
about 7.6 cm.
The large intestine
consists of the cecum,
colon, rectum, and anus
The large intestine (or colon) is
used to absorb water from the
waste material leftover and to
produce vitamin K and some B
vitamins using the helpful bacteria
that live here.
 All leftover waste is compacted
and stored at the end of the large
intestine called the rectum.
 When full, the anal sphincter
loosens and the waste, called
feces, passes out of the body
through the anus.
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