The structure of placental villi is complex and includes several layers. The outermost layer is the syncytiotrophoblast, which is a multinucleated cell layer that forms the main barrier between maternal and fetal blood. Beneath this layer lies the cytotrophoblast, composed of individual trophoblast cells. The core of the villus contains mesenchymal cells, fetal blood vessels, and macrophages known as Hofbauer cells.
