Aim: How do humans develop from a
zygote to a fetus?
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Fertilization may
occur within a few
days of ovulation
The fusion of the
sperm nucleus and
the egg nucleus result
in a diploid zygote.
Fertilization occurs in
the _______________.
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In the first week after
fertilization, the
zygote undergoes a
series of mitotic
divisions known as
cleavage.
Cleavage produces
many smaller cells
within the zygote.
Cleavage continues as the zygote moves through the
Fallopian tube toward the uterus.
When the zygote is a solid ball of cells, it is called a
morula.
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By the time it reaches the uterus, the zygote is a
hollow ball of cells called the blastocyst.
The blastocyst attaches itself to the lining of the
uterus in an event called implantation.
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Once the blastocyst
has been implanted
into the uterus,
differentiation occurs.
Differentiation (also
called spcialization) is
when the cells of the
blastocyst develop
into the various types
of tissues in the body.
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Differentiation is
caused by the
activation of certain
genes.
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The next stage of
development is
gastrulation.
During gastrulation,
three distinct cell
layers form.
The ectoderm
 The mesoderm
 The endoderm
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Development of Organs and
Organ Systems
ECTODERM
MESODERM
ENDODERM
Nervous system
Bones and
muscles
Lining of
digestive tract
Epidermis of skin, Blood and blood
sweat glands, hair vessels
and nails
Lining of trachea,
bronchi and lungs
Reproductive and Liver, pancreas
excretory systems