Final answer:
The hormone that maintains the corpus luteum's secretion of estrogen and progesterone following implantation is 1) human chorionic gonadotropin (hCG).
Step-by-step explanation:
The hormone released from the chorionic portion of the placenta which maintains corpus luteal secretion of estrogen and progesterone following implantation is human chorionic gonadotropin (hCG). This hormone is crucial as it directs the corpus luteum to survive, enlarge, and continue producing progesterone and estrogen to suppress menses, creating a suitable environment for the developing embryo. The presence of hCG allows the blastocyst to remain implanted in the uterine wall by ensuring the continuous support of the corpus luteum until the placenta can take over the hormone production necessary for pregnancy maintenance.