The blastula's implantation in the endometrial lining leads to the formation of which structure?

The implantation of the blastula in the endometrial lining primarily leads to the formation of the placenta. The placenta is an essential organ that develops during pregnancy and is responsible for facilitating the exchange of nutrients, gases, and waste products between the mother and the developing embryo or fetus.

Once the blastula implants into the uterine wall, it begins to differentiate into two main structures: the embryonic tissues and the extra-embryonic tissues. The extra-embryonic structures include the chorion, which develops into the outermost layer of the placenta, as well as the amnion and the yolk sac. However, the placenta itself forms specifically as a result of the interactions between the chorionic tissue and the maternal endometrium.

Through this implantation process, the chorion ultimately helps establish the placental structure, which is vital for the sustenance of the embryo, allowing for the transfer of nutrients and oxygen while also removing carbon dioxide and waste products. Therefore, the correct answer, indicating that implantation leads to the formation of the placenta, accurately reflects the biological processes involved in early pregnancy.