Practice question

Upon implantation, trophoblast differentiates into mononuclear cytotrophoblast stem population and multinucleated syncytiotrophoblast formed by cell fusion mediated by endogenous retroviral syncytins. Syncytiotrophoblast directly invades maternal decidua, erodes vessels creating intervillous spaces filled with maternal blood, secretes chorionic gonadotropin sustaining corpus luteum, and forms outer layer of chorionic villi constituting fetal component of placenta. Its transporters facilitate nutrient glucose amino acid exchange. Thus syncytiotrophoblast underlies construction and maintenance of hemochorial placentation crucial for fetal support, immune tolerance, endocrine regulation throughout gestation and maternal-fetal communication.