Final answer:
The two sections of cells that the blastocyst divides into before implanting into the uterine wall are the embryoblast (inner cell mass) and the trophoblast (outer cell layer). The embryoblast develops into the embryo, and the trophoblast forms part of the placenta.
Step-by-step explanation:
The blastocyst divides into two sections of cells before implanting itself into the uterine wall. These sections are known as the embryoblast (inner cell mass) and the trophoblast (outer cell layer). The embryoblast will develop into the embryo itself, while the trophoblast will implant in the uterus and eventually evolve to form the placenta and other necessary embryonic tissues.
The blastocyst reaches the uterus approximately 4 to 5 days after fertilization, and implantation occurs about a week after fertilization. The trophoblast begins the process by contacting the cells of the endometrium lining the uterus. As the blastocyst prepares for implantation, the fluid-filled cavity known as the blastocoel, or blastocoele, is maintained by trophoblast cells which continue secreting fluid.