The menstrual cycle involves monthly ovulation and shedding of the uterine lining. It is regulated by hormones from the hypothalamus, pituitary gland, and ovaries in a feedback loop. During the cycle, the endometrium and follicles develop in phases. In the early follicular phase, menstruation occurs and follicles begin to mature under rising FSH levels. Near mid-cycle, an LH surge causes ovulation from the dominant follicle. In the luteal phase, the corpus luteum secretes progesterone and estrogen to prepare the uterus for potential implantation. Without pregnancy, progesterone levels fall, triggering menstruation.

1. The Endocrine Cycle and the Physiology of the Menstrual Cycle