The embryo's heart is the
first organ that forms. It is derived from two
primitive heart tubes. Between days 18 to 30,
the primitive heart tubes fuse together, bend
and twist to form a simple version of the heart.
About half way through this process, the heart
starts to beat. At 2 months, the heart bears
a close resemblance to what it will look like
after the baby's born.
The resemblance
is only superficial since the inside of the heart
is different in both form and function. In a
newborn's heart, oxygen-poor blood from
the body enters the right atrium, goes to the
right ventricle where it is pumped to the lungs
to become rich with oxygen. From the lungs, the
blood flows back to the heart filling the left
atrium then enters the left ventricle. The left
ventricle pumps the oxygen rich blood through
the aorta, which carries it to the rest of the
newborn's body.
The fetal heart has the
same basic components as the newborn heart, but
there are a couple important differences. Because
the placenta is providing all of the oxygen the
fetus requires, its lungs are not needed to perform
this task. Much of the fetus' blood is
detoured away from the lungs through two openings
or connections: the foramen ovale, which connects
the right and left atria, and the ductus arteriosus,
which connects the aorta and the pulmonary artery.
These two important connections will remain open
up until the time of birth.
Within thirty minutes
after the baby's first breath, the ductus
arteriosus will completely close, and the flap
of the foramen ovale will shut off like a valve.
This happens because of an increase in pressure
on the left side of the heart, and a decrease
on the right side. These changes in the heart
anatomy cause the blood to flow to the lungs,
which will take over their lifelong job of supplying
oxygen to the body.
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