This essay, Development of the Human Placenta, talks about pacenta which is a fetomaternal organ that serves as a connection between mother and the developing fetus. The primary function of which is to carry nourishment and remove the waste products from the fetus. …
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According to the report blastomeres are separated into two parts by the blastocystic cavity, namely the trophoblast and the inner cell mass also called as embryo blast. Implantation is the first step in the development of placenta. Approximately at 6th day after fertilization the blastocyst attaches to the endometrium and the process of implantation begins. Now the trophoblast layer of the blastocyst at the embryonic pole gets differentiated into two layers, an inner layer called cytotrophoblast and an outer layer called as syncytiotrophoblast. Syncytiotrophoblast is highly invasive and expands quickly adjacent to the embryoblast, it produces enzymes that erode the maternal tissue enabling the blastocyst to burrow into the endometrium. The endometrial cells undergo apoptosis that facilitates invasion. The process of implantation is completed by the end of second week and the blastocyst is superficially implanted in the endometrium.This essay discusses that at about day 10 blood filled lacunae appear in the syncytiotrophoblast which ultimately fuse at day 12 to form the lacunar network, the primordia of intervillous spaces of placenta,synsytiotrophoblast erodes the endometrial capillaries and maternal blood flows into these capillaries giving rise to the primordial utero placental circulation. Villi that attach to the maternal tissues through the cytotrophoblastic shell are termed as stem villi from which the branch villi project. The decidua basalis is divided into many cotyledons by the placental septa, formed by the primary chorionic villi during erosion of the decidua basalis by them. Each cotyledon consists of one stem villus that gives rise to many branch chorionic villi and it is through the walls of these branch villi that the actual exchange of materials between the blood of mother and fetus occurs. At 20 weeks of pregnancy complete external membrane is formed consisting of amnion, chorion and decidua.
Both maternal and fetal parts of placenta play role in immunoregulation that helps to protect the fetus from immune attack by the mother as the fetal part of placenta consists of both maternal and paternal genes that is it is an allograft, still it is not rejected by the mother’s immune system because of several reasons;
1. Trophoblastic cells express on their surface class I antigens including HLA-G that are nonpolymorphic and play role in allograft protection.
2. Syncytiotrophoblast of chorionic villi do not express MHC antigens on their surface and thus do not evoke an immune response.
3. Endometrium secretes certain immunosuppressive molecules for e.g; PGE2, TGF B and IL-10.
4. Ligands present on the trophoblast induce apoptosis of activated maternal leukocytes.
5. Increased percentage of CD 8+ cells and decrease in ratio of CD4+/CD8+ cells was found in distant and regional lymphatic organs during pregnancy.
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