Menstrual cycle

the period in which an ovum matures, is ovulated, and enters the uterine lumen via the fallopian tubes; ovarian hormonal secretions effect endometrial changes such that, if fertilization occurs, nidation will be possible; in the absence of fertilization, ovarian secretions wane, the endometrium sloughs, and menstruation begins; this cycle lasts an average of 28 days, with day 1 of the cycle designated as that day on which menstrual flow begins