trophoblast, trophoblastic The cell layer that forms the outer wall of the blastocyst. It supplies the embryo with nutrients and aids with implanting the embryo in the uterine wall. In mammals, a layer of tissue formed by cells forming the outer covering of the blastocyst. After implanation of the blastocyst, this layer is no longer cellular. At t... Found on http://www.wordinfo.info/words/index/info/view_unit/2191/9