Human placentation is characterized by the development of a hemochorial placenta and
concomitantly by considerable changes in the vasculature of the uterus. The trophoblast is an essential
tissue of the placenta. After blastocyst implantation, it differentiates into villous trophoblast, which
ensures exchanges between mother and fetus as well as the endocrine functions of the placenta, and into
invasive extravillous trophoblasts, which anchors the placenta in the uterus and participate to the
implementation of the utero placental vascularization. We describe here the different stages of the
placental morphogenesis and the physiological mechanisms responsible for uterine vascular
remodeling. We then consider the main functions of the human placenta and in particular the qualitative
and quantitative evolution along pregnancy of trophoblast hormonal functions from a paracrine role
during the first trimester of pregnancy involved in the quality of placentation to an endocrine role that
allows uterine quiescence and maternal adaptation to pregnancy.
Keywords: Syncytiotrophoblast, invasive extravillous cytotrophoblasts, hormones, preeclampsia, fetal
growth.
