n. the tissue that forms the wall of the *blastocyst. At implantation it forms two layers, an inner cellular layer (cytotrophoblast), which does not invade maternal tissue and forms the outer surface of the *chorion; and an outer syncytial layer (syncytiotrophoblast, or plasmoditrophoblast), which erodes the maternal tissue and forms the chorionic *villi of the placenta. See also gestational trophoblastic disease.... trophoblast
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