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Capítulo 41 4 a 5 Meses (16 a 20 Semanas): Resposta ao Estresse, Verniz Caseoso, Ritmos Circadianos
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| By 16 weeks, procedures
involving the insertion
of a needle into the abdomen
of the fetus
trigger a hormonal
stress response
releasing noradrenaline,
or norepinephrine,
into the bloodstream.
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| In the respiratory system,
the bronchial tree
is now nearly complete.
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| A protective white substance,
called vernix caseosa,
now covers the fetus.
Vernix protects the skin
from the irritating effects
of amniotic fluid.
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| From 19 weeks fetal movement,
breathing activity,
and heart rate begin
to follow daily cycles
called circadian rhythms.
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Capítulo 42 6 a 7 Meses (24 a 28 Semanas): Reflexo Cócleo-Palpebral e de Sobressalto; Pupilas Respondem à Luz; Olfato e Paladar
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| By 20 weeks the cochlea,
which is the organ of hearing,
has reached adult size
within the fully developed
inner ear.
From now on,
the fetus will respond
to a growing range of sounds.
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| Hair begins to grow
on the scalp.
All skin layers and structures
are present,
including hair follicles
and glands.
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| By 21 to 22 weeks
after fertilization,
the lungs gain some ability
to breathe air.
This is considered
the age of viability
because survival
outside the womb
becomes possible
for some fetuses.
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