embryo cord endometrium digestive ninth embryo amniotic lining liquid grow blood sac birth fetus placenta systems uterus lungs organs seventh move embryo umbilical
First
Trimester
:
The
zygote
begins
to
divide
into
several
cells
and
an
forms
.
The
attaches
to
the
of
the
uterus
(
)
.
The
forms
around
the
embryo
.
It
is
a
membrane
full
of
that
protects
the
embryo
.
The
placenta
forms
at
this
time
.
The
is
an
organ
that
permits
the
exchange
of
substances
between
the
mother's
and
the
through
the
.
Second
Trimester
:
The
embryo
becomes
a
.
It
grows
and
all
the
begin
to
form
inside
.
It
starts
to
take
on
human
form
and
begins
to
.
Third
Trimester
:
The
fetus
continues
to
and
mature
.
After
the
month
,
the
development
of
the
body
is
complete
,
although
the
and
are
not
yet
mature
.
Around
the
month
,
the
fetus
engages
with
the
head
towards
the
opening
of
the
,
in
preparation
for
.