What is the function of the menstrual cycle?

its the series of changes a woman's body goes through to prepare for a pregnancy. About once a month, the uterus grows a new lining to get ready for an egg. When there is no fertilized egg to start a pregnancy, the uterus sheds its lining.

The proliferative phase is the second phase of the uterine cycle when estrogen causes the lining of the uterus to grow, or proliferate, during this time. As they mature, the ovarian follicles secrete increasing amounts of estradiol, and estrogen.