syncyotrophoblast

The syncytiotrophoblast is a multinucleated cell layer formed by the fusion of cytotrophoblast cells in the early embryo. It covers the entire surface of the chorionic villi and constitutes the outermost layer of the placenta. By forming a continuous syncytial membrane, the syncytiotrophoblast provides a large surface area for maternal-fetal exchange of gases, nutrients, and waste products. It also secretes crucial hormones such as human chorionic gonadotropin, which maintains the corpus luteum during the early stages of pregnancy, and placental lactogen, which modulates maternal metabolism.

The syncytiotrophoblast actively transports ions and molecules from maternal blood into the fetal circulation through specialized transporters and facilitates the diffusion of oxygen and carbon dioxide. It undergoes continual shedding of microvilli, a process that releases syncytial nuclear fragments into maternal circulation. These fragments can be detected in maternal blood as a diagnostic marker for gestational trophoblastic disease or preeclampsia.

Histologically, the syncytiotrophoblast appears as a thick, uniform layer of fused nuclei without cell borders. Its integrity is essential for maintaining barrier function and endocrine activity of the placenta. Disruption or abnormal proliferation of the syncytiotrophoblast is implicated in various pregnancy complications, including intrauterine growth restriction, preeclampsia, and certain forms of fetal demise.