Embryology at a glance

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Embryology at a glance

• Watch this
• Then this

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D. Cavitationand the Blastocyst Next a
fluid-filled
inner cell mass
forms
between the inner cell mass
This is called
This gives rise to
the blastocyst
blastocyst germ-bag
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The
the epiblast
the hypoblast This is called the
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Week 2 BilaminarDisk Formation (2a)
it becomes filled with
this will eventually
surround and suspend the embryo and provide
a shock-free environment
a constant temperature and allow free
movement
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Week 2 BilaminarDisk Formation (2b)
The cells lining the amniotic cavity are shed
on occasion These cells, along with
proteins, carbohydrates, fat, enzymes, hormones
and embryonic excretions can be extracted and
examined
This procedure is called an
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Week 2 BilaminarDisk Formation (3)
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(1)
Forms lining of GI tract
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Week 3 Gastrulation(2)
The epiblastis now
The hypoblast is now
The middle layer,
composed of cells that migrated from the
epiblast, becomes the mesoderm
These 3 cell layers give
rise to all the cells of your body!
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Week 3 Gastrulation(3a)
The
will give rise to
skin
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Week 3 Gastrulation(3b)
plus outgrowths of the digestive tract that give

rise to the
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Week 3 Gastrulation(3c)
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While the external look of a human is called
bilateral symmetry because if you cut us in half
on the median plane, both sides look roughly
exact. However, our internal design is called
tube within a tube as seen here.
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Four Weeks

Figure 297a, b
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Eight Weeks
By the end of
formed
now begins to look human-like
(The fetus
remains at very high risk of malformations
through the 8th week)
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Twelve Weeks
This is the
period of functional maturation of all organ
systems
(By this age, the
fetus is at lower risk of malformations)
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HOMEWORK

• What are the three germ layers and what mature
  features do they form?