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Nourishment and protection of a maturing fetus are provided by the fetal placenta. The tough tissue structure also plays roles in gas exchange, removal of waste, and fighting of disease. It is comprised of a maternal portion that attaches to the mother's womb and a fetal portion that attaches to the fetus. Villi, blood vessels, and the umbilical cord are some of the components contained within and around the placenta.
Development of the fetal placenta begins immediately after an embryo begins growing. This process takes place during early embryo cell division. The outermost layer of the pre-embryo becomes a nourishing lining of cells called a trophoblast that attaches to the uterus. This structure will eventually develop into a large portion of the placenta.
The fetal placenta consists of a section for the fetus and a smaller section attached to the mother. The former is called the villous chorion, whereas the latter is referred to as the decidua basalis. These two structures are held together by structures known as villi. Blood passing through the villi brings nutrients and oxygen to the fetus while also taking away waste and carbon dioxide. Much of the blood flow takes place via the blood vessels contained in the umbilical cord: the structure that connects the fetus to the placenta.
Immunity to disease constitutes another important purpose of the placenta. On some occasions, the immune system of the mother actually attacks the fetus as a harmful invader. In order to defend against these potential attacks, the placenta creates lymphocyte immune cells and a substance called neurokinin B.
Additionally, a fetus is enclosed in a protective amniotic sac, and part of which is considered part of the placenta. The umbilical cord and various small blood vessels also reside within this set of tough tissues. The placental sac is both flat and smooth, and it is filled with fluid that provides protection for the fetus, allows movement, and also regulates fetal temperature. It separates the blood supplies of the mother and the fetus.
Fetal placenta structures are primarily found in animals that give birth, especially mammals. They do also appear in some types of lizards and snakes, however. When a fetus is delivered, the placenta is also expelled during the childbirth. A human placenta is generally small and lightweight. It stands around nine inches (22 centimeters) tall and weighs about one pound (500 grams).
Several unorthodox beliefs and uses have surrounded the fetal placenta. Some cultures revere the structure and bury it with their dead. Others believe that consuming the placenta will instill individuals with special powers or good health. Some even maintain that the placenta is a reincarnation of dead relatives. In more conventional medical practices, the stem cells derived from placentas are believed to hold potential for treatment of a number of conditions.
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