Fetal Development




Fertilization
Fetal development starts with the process of
fertilization. It starts when the female ovulates producing
an egg. This egg then travels into the fallopian tube where
it waits to be fertilized. Once sperm enter the body they
must travel up the uterus until they make their way up to
the egg. Once at the egg the sperm try to get in. They
sperm wiggle their tails until they make it in. Once it
makes it in the egg will not any other sperm in. The sperm
that made it then drops its tail. After about twenty hours
inside the egg the sperm finds the nucleus of the egg and
fuses with it. Now the egg has all the genetic material
that it needs to make a new human being. It nows begins to
move down into the uterus. The egg is now called a
blastocyst. The time that this takes is often measured
after the last menstrual period(LMP). The time is also
measured in trimesters, three month intervals.
After about thirty hours the cell divides for the first
time. It is continuously moving towards the uterus where it
will call home for the next nine months. After about two
days it has divided to having about eight cells. After four
days it is in the uterus and has to "land" somewhere and
attach itself to the endometrium. The eighth day is when
implantation occurs. The fertilized egg then implants
itself on the endometrium, the uterine lining, and begins to
grow. The cell begins to grow and develop. By the 12th
day the blastocyst has approximately two thousand cells in
it. It has had time to attach itself to the endometrium and
these anchors are called protuberances.
Embryonic Development
After about three weeks the tiny little heart is
developed enough to start beating and has the ability to
pump blood. At this time the blastocysts becomes an embryo.
There are three layers that form the embryo. These layers
are called the germ or cell layers. The outer cell layer
will eventually become the backbone, the brain, and the
nerves. This layer also makes the skin, the hair, and
sebaceous and sweat glands.
The middle layer is going to be the lower layer of
skin, the bones, and the muscles. Blood and lymph vessels
are also made from this layer. Blood cells and the heart
muscles make a "primitive bloodstream (Nilsson, 1990, p.
77)." The sex organs and the kidneys also come from this
layer.
The inner layer makes up the a simple intestinal tube
with a mucus membrane. From that tube the lungs and urinary
tract form. Everything from all the layers then come
together to form the organ system. Then the embryo can do a
test run with the system. This happens every day while the
organs are being formed.
At around four weeks from the LMP the embryo begins to
form a backbone. The bones are split in two, half on each
side. The nerves begin to form down the middle of the bone
pieces. The placenta is by now drawing nutrients from the
mother. The nutrients then go down the umbilical cord into
the embryo. The wastes then go into the mother where they
are discarded.
After about five weeks from the LMP the embryo is
visible to the world outside. The doctors can look at the
embryo and measure it. The length is called the crown-rump
length. The sixth week is when the measurements are
normally taken.
Everything is continually growing and the whole body
straightens up. The head makes up about one-third of the
embryo\'s body. There is still no skull so you can see the
brain. The arms as well as the legs are very short. This
is because the embryo grows from the head down to the toes.
That means the head is going to be huge compared to the rest
of the body.
After six weeks from the LMP the embryo\'s backbone has
come together and there are two arteries that run down each
side of it. The skin on the embryo is very thin and
translucent. The placenta and the embryo are connected by
the umbilical cord. The one large artery and two smaller
veins run through the umbilical cord. Everything that the
embryo needs will come through the umbilical cord.
Fetal Development
After about eight weeks from the LMP the tiny little
embryo has every organ that it needs. The embryo is now
referred to as a fetus. The risks of miscarriages and
malformations has greatly been reduced. The brain is
visible from the outside of the fetus. It still isn\'t
controlling the fetus because it has not been fully
developed yet.
By the third month the