The placenta

In mammals, the blastocyst defines with the maternal organism, a structure which allows embryonic development during gestation: the placenta. The plac enta is a multi-functional organ, the role of which in fetal growth can be paralleled to that of the lungs, the kidneys and the intestine during adult life. in this review, we briefly describe the different types of placentat ion before focusing on the specificities of the human placenta. Human pregn ancy is indeed characterized by a total decidualization of the uterus, a ma jor invasiveness of the extravillous trophoblast. In addition, in human pla centa, steroid and protein hormones are produced by the villous trophoblast in great amounts, unparalleled in placentae of other mammals. The major co mplication of pregnancy is preeclampsia, which is often associated with fet al intrauterine growth retardation, and is of pla cental origin. However, d espite the key role of the placenta in fetal development, the molecular and cellular mechanisms involved in its development remain poorly known.