part of part of develops into develops into extraembryonic cell trophoblast cell trophectodermal cell trophectoderm cell An extraembryonic cell that is part of the trophectoderm, representing the first lineage to differentiate in the embryo. This cell is crucial for implantation into the uterine wall and differentiates into trophoblast cells, which contribute to placenta formation and facilitate maternal-fetal nutrient and signal exchange. trophectoderm