Final answer:
Progesterone, produced by the corpus luteum, prepares the endometrial lining for implantation and inhibits further ovulation. If implantation of a fertilized egg does not happen, progesterone levels fall, initiating menstruation.
Step-by-step explanation:
The hormone that prepares the endometrial lining of the uterus for potential implantation is progesterone. Progesterone is produced by the corpus luteum after ovulation and plays a crucial role in maintaining the endometrium. This hormone helps to thicken the endometrial lining, making it receptive to a fertilized egg, and it also inhibits the release of further FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone) to prevent the development of more eggs and follicles during this critical time. If implantation does not occur, the corpus luteum degenerates, leading to a decrease in progesterone levels, which causes the endometrial lining to break down and menstruation to begin, starting the next menstrual cycle.