Final answer:
The embryo implants into the endometrium of the uterus. Implantation typically occurs one week after fertilization, with the blastocyst embedding into the endometrium. This process is vital for pregnancy and is confirmed by the hormone ß-HCG.
Step-by-step explanation:
The embryo implants into the endometrium of the uterus. This process, known as implantation, is critical for establishing a successful pregnancy. After fertilization, the zygote becomes a blastocyst, which travels down the fallopian tube and reaches the uterus. Approximately a week after fertilization, the outer cells of the blastocyst, the trophoblast, contact cells of the endometrium and begin embedding into it. The embedment of the blastocyst into the endometrium essentially concludes the pre-embryonic stage of development. Successful implantation is indicated by the release of the hormone human beta chorionic gonadotropin (ß-HCG), which is also the hormone detected by pregnancy tests.
Most successful implantations occur in the fundus or on the posterior wall of the uterus. However, if the endometrium is not in an ideal state to receive the blastocyst, the blastocyst will attempt to find a better spot or might fail to implant successfully, leading to the blastocyst being shed with the endometrium during the menstrual cycle. On successful implantation, the endometrium grows over and surrounds the embryo, securing it to the uterine lining.