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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. 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 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 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 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 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 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 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.
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 By the third month the organ and organ systems are becoming interconnected. The brain is starting to take over the functions of the organs.
The yolk sac is forming the At the fourth month the fetus is over ten centimeters long. It only weighs about twenty grams though. The face is starting to form and look more human. The five outgrowths that make up the face are moving into position. One of them make up the nostrils and nose and the middle of the upper lip. Two of the other outgrowths come from up under each eye and form the cheeks and the rest of the upper lip. The other two formed the lower lip and the chin. The eye forms when the forebrain issues a hollow stalk on both sides of the brain. The stalks start to thicken on the end and this becomes the eyeball.
The iris grows from the edges in. Then the skin grows over the eye and this The ear grows from three different parts. From the skin a hollow area forms and this will be the inner ear. A little after that the outer ear develops and the middle ear then forms. Around the end of the fourth month the fetus can hear sounds that come from the mother and the outside The arm and the foot are formed by from little buds that stick out from the body. These little buds keep growing to form the arms and legs.
At the end of the buds there are little flipper like formations that will be the hands and feet. The arms will get longer before the legs will. After about the third month the hands can grab things and the feet can kick. The kicks are usually to small for The bones form from cartilage which is what is initially formed in the fetus while it is still in the uterus. The skull bones are flexible and they can be damaged during labor. Sometimes collarbones and arm bones can be broken and this really doesn't cause much concern because they just heal themselves.
The bones usually heal without scars or any traces of breakage. During the third month after the LMP little hairs appear on the fetus. "The fetus's body starts growing a fine hair called lanugo (from the Latin lana for fine During the first few months of development you cannot tell apart the male from the female by looking at them. A small bud forms between the legs which will form the male penis or the female clitoris. A swelling forms on either side of the bump which will be the scrotum in boys. In girls a slit will form and this will become the vagina. The testicles form deep inside the abdomen.
The male can produce sperm right up to an old age. The ovaries already have all the eggs that the women will ever need in her life. Approximately half way through the pregnancy the mother can start to feel the fetus kicking inside of her. Then after a couple more weeks the fetus has grown to little over a pound. The fetus can see some light as it comes through the abdominal wall. "The fetus may frequently suck its thumb" (Silverstein, Silverstein, and Silverstein, 1994, During the seventh month after the LMP the fetus starts to put on weight.
The weight of the fetus increases by nearly half a pound a week. the mother has to watch her weight because overeating during pregnancy can be bad for the fetus. If the mother doesn't eat enough the fetus ....
Research essay sample on Fetal Development