Final answer:
Estrogen is the hormone responsible for causing the regrowth of the endometrial lining of the uterus, which is important for the menstrual cycle and preparation for potential pregnancy.
Step-by-step explanation:
The hormone that causes the regrowth of the endometrial lining of the uterus is estrogen. During the menstrual cycle, estrogen is responsible for rebuilding the endometrium that has been shed during menstruation. After ovulation occurs and an egg is released, both estrogen and progesterone are secreted by the corpus luteum. While estrogen assists in the initial regrowth of the endometrium, progesterone then further prepares the endometrial lining for potential implantation of an embryo by thickening it and maintaining the endometrium if pregnancy occurs. If pregnancy does not occur, both estrogen and progesterone levels drop, leading to menstruation where the lining is shed. Therefore, in the context of the menstrual cycle and the preparation for possible pregnancy, both estrogen and progesterone play crucial roles, with estrogen being pivotal for the regrowth of the endometrial lining.