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Desenvolvimento Embrionário: 4 a 6 Semanas
Capítulo 11 4 Semanas: Líquido Amniótico
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| By 4 weeks
the clear amnion
surrounds the embryo
in a fluid-filled sac.
This sterile liquid,
called amniotic fluid,
provides the embryo
with protection from injury.
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Capítulo 12 O Coração em Ação
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| The heart typically beats
about 113 times per minute.
Note how
the heart changes color
as blood enters and leaves
its chambers with each beat.
The heart will beat
approximately
54 million times before birth
and over 3.2 billion times
over the course
of an 80-year lifespan.
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Capítulo 13 O Crescimento do Cérebro
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| Rapid brain growth is evidenced
by the changing appearance
of the forebrain,
midbrain,
and hindbrain.
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Capítulo 14 Brotos dos Membros
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| Upper and lower limb
development begins
with the appearance
of the limb buds by 4 weeks.
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| The skin is transparent
at this point
because it is only
one cell thick.
As the skin thickens,
it will lose this transparency,
which means that we will only
be able to watch internal organs
develop for about another month.
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Capítulo 15 5 Semanas: Hemisférios Cerebrais
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| Between 4 and 5 weeks,
the brain continues
its rapid growth
and divides
into 5 distinct sections.
The head comprises about 1/3
of the embryo's total size.
The cerebral
hemispheres appear,
gradually becoming
the largest parts of the brain.
Functions eventually controlled
by the cerebral hemispheres
include thought, learning,
memory, speech, vision,
hearing, voluntary movement,
and problem-solving.
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Capítulo 16 Vias Respiratórias Principais
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| In the respiratory system,
the right and left main stem
bronchi are present
and will eventually connect
the trachea, or windpipe,
with the lungs.
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Capítulo 17 Fígado e Rins
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| Note the massive liver
filling the abdomen
adjacent to the beating heart.
The permanent
kidneys appear by 5 weeks.
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Capítulo 18 Saco Vitelino e Células Germinativas
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| The yolk sac contains
early reproductive cells
called germ cells.
By 5 weeks
these germ cells migrate
to the reproductive organs
adjacent to the kidneys.
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Capítulo 19 Placas da Mão e Cartilagem
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| Also by 5 weeks,
the embryo develops
hand plates,
and cartilage formation begins
by 5 1/2 weeks.
Here we see
the left hand plate
and wrist at 5 weeks and 6 days.
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