What structure implants into the endometrium?

The blastocyst is the correct structure that implants into the endometrium, which is the inner lining of the uterus. After fertilization, a zygote undergoes several cell divisions to form a morula, which is an early stage of development made up of a solid ball of cells. The morula then transforms into a blastocyst, which consists of an inner cell mass (that will eventually develop into the embryo) and an outer layer of cells known as the trophoblast.

As the blastocyst reaches the uterus, it is at this stage that it adheres to the endometrium and begins the process of implantation. The trophoblast cells play a crucial role in this process, as they invade the endometrial lining, facilitating attachment and establishing nutrient exchange necessary for embryonic development. This implantation is a vital step for establishing a successful pregnancy.

In contrast, the oocyte is the female gamete that is released from the ovary and does not implant into the endometrium. The chorion, which develops from the trophoblast after implantation, contributes to the formation of the placenta but is not the initial structure that implants. The morula, as an early developmental stage, does not engage in the implantation process either,