Answer
During blastocyst morphogenesis from morula, two populations of cells are differentiated-- the outer cells that form the walls of the blastocyst, and an inner embryoblast or inner cell mass which will form the structures of the embryo.
The combining form "tropho-" means to nourish or nourishment, and one of the functions of the trophoblast is to supply nourishment to the blastocyst. In addition, the trophoblast gives rise to the chorionic membrane, and forms the fetal contribution to the placenta.
Work Step by Step
On the eighth day after fertilization, at the area of contact of blastomeres and endometrium, the trophoblast differentiates into two layers--the cytotrophoblast and the syncytiotrophoblast-- both of which become parts of the chorion. The syncytiotrophoblast secretes enzymes that facilitate the burrowing of the blastocyst into the uterine wall -- endometrium and myometrium.
The trophoblast also helps to maintain the secretory activity of the endometrium, and it suppresses of uterine motility. In addition, human chorionic gonadotropin (hCG) is secreted by the trophoblast. This LH-like hormone targets the corpus luteum (CL) and keeps it from deteriorating. The estrogen produced in response keeps the endometrium secreting, and the progesterone keeps the myometrium calm; this prevents premature expulsion of the conceptus.
At about the ninth week of gestation, the job of maintaining the pregnancy passes from corpus luteum to a newly functional placenta.
