An overview of the placenta

Placenta is the post-mammals and mammals during pregnancy by the embryo of the embryo and maternal endometrium combined growth of the mother-child exchange of substances in the transitional organ. The fetus develops in the womb, relies on the placenta to obtain the nutrition from the maternal body, but both sides maintains the quite independence. Placenta also produces a variety of hormones to maintain pregnancy, is an important endocrine organ. Some reptiles and fish to reproduce the offspring of viviparous manner, the embryo growth of some ancillary structures such as yolk sac, gill and other closely integrated with the mother tissue in order to achieve the exchange of material between mother and child, such a structure called false placenta. Placenta after childbirth, or blindly traditional Chinese medicine, known as human placenta, Placenta.

Placenta is the mother and fetus for the exchange of material between the organ, is the embryo and maternal organization combination, by the amniotic membrane, chorion frondosum and the end of the decidua. Placenta, also known as the sub-clothing, clothing cell, Placenta, fetal clothing, fetal membranes.

Placenta formation

Placenta The placenta consists of amniotic membrane, lamellar chorion (also known as dense chorionic villi) and the end of the decidua.

1. amniotic membrane: the part of the fetus that constitutes the placenta, the placenta is the innermost layer. The amniotic membrane is a translucent membrane attached to the surface of the chorionic membrane. Amnion smooth, no blood vessels, nerves and lymph, with a certain degree of flexibility. Normal human amniotic thickness 0.05mm.

2. chorionic villus: constitute the fetal part of the placenta, accounting for a major part of the placenta of pregnancy.

Embryo development to 13 ~ 21 days, the main structure of the placenta - villi gradually formed. About 3 weeks after fertilization, when the villi within the blood vessels, the establishment of fetal placental circulation.

With the end of decidua in contact with villi, due to nutrient-rich well-developed, known as leaf-like chorion. Villous terminal end of the placenta suspended in the maternal blood gap between the villi called the free hair, long into the bottom of the decidua, said the fixed villi. The placenta grows out of the decidua, and the fetal leaves are not completely separated into maternal leaves. Each maternal leaf contains several fetal leaves, each of which has its own spiral artery supplying blood.

Pregnant uterus spiral artery (also known as uterine placental artery) through the decidual plate into the maternal leaves, the material exchange between mother and child are in the fetal lobular villi Department, indicating that the fetal blood is through the umbilical artery until the villi capillaries, Maternal blood in the gap for material exchange, the two are not directly connected. Villous tissue structure: full-term pregnancy placental villous trophoblast cells mainly composed of syncytiotrophoblast, cytotrophoblast cells scattered only in the visible, the inner layer of the trophoblast for the basement membrane, the role of the placental barrier.

3. Decidua: constitute the maternal part of the placenta, accounting for a small part of the placenta of full-term pregnancy. The bottom of the decidual surface covered with a layer of the villi from the fixed trophoblast cells and decidua together to form the bottom of the villi gap, called the decidual plate, from the plate to the direction of the chorion out some decidual interval, generally not more than placenta full 2/3 of the thickness, the maternal face of the placenta is divided into about 20 maternal leaves visible to the naked eye.

The immunological properties of placenta

Fetus and placenta both maternal genetic material also has parental antigen material. Therefore, the fetus and fetal membranes are equivalent to allografts for the mother. But why the fetus can grow and develop in the mother's womb, not be excluded, the nature of its immune tolerance is what, this is for many years has been around the medical scientists and caused great interest in a complex problem.

Some scholars believe that early embryo and fetal membranes tissue without antigenicity, and thus with some of the early embryo tissue transplantation, does not cause immune rejection. Some studies have shown that fetal histocompatibility antigen does not express in the trophoblast surface, but only in placental tissue and placental vascular endothelial cells on the expression of placenta, so syncytial trophoblast cells from the blastocyst into the mother, it will not Causing immune rejection. With embryonic development, embryonic tissue began to antigen, and from weak to strong, to the full term of the fetus, followed by a strong immune rejection, childbirth started.

As the separation of maternal and fetal blood circulation, coupled with the development of the fetus and maternal interface, the villi surface or placental syncytiotrophoblast cell surface, often with a thick layer from the maternal circulatory system of fibrin and fibrin-like substances deposition and cover , Constitute an immune barrier. The trophoblast cell surface antigens are masked or trophoblast cells can not effectively express its antigen, preventing the fetal antigen and maternal lymphocytes and maternal anti-trophoblast antibody contact, and therefore does not cause immune rejection.

According to reports, the placenta produced HCG, estrogen, progesterone and maternal production of adrenal cortex hormones, inhibit the role of rejection.

Recent experiments have shown that early in fertilization, the mother's serum that there is an immunosuppressive factor, known as the early pregnancy factor (early pregnancy factor, EPF). People's fertilized eggs in fertilization 24 hours to produce early pregnancy factor. Early pregnancy factor can inhibit the activity of maternal lymphocytes, which may have a special role in the prevention of immune rejection of blastocysts. At present, foreign clinical use of early pregnancy factors have been used as indicators of fertilization monitoring.