The female reproductive cycle, also known as the menstrual cycle, occurs regularly in fertile women and involves changes in the hypothalamus, pituitary gland, ovaries, and endometrium. The average cycle is 28 days and includes the menstrual, proliferative, ovulatory, and secretory phases. During the cycle, levels of hormones like estrogen and progesterone rise and fall, regulating the thickening and shedding of the uterine lining. If pregnancy does not occur, menstruation begins and the cycle repeats.