Menstruation, or Menorrhea, (most commonly called a period) is the monthly blood flow that discharges from a woman's uterus. This process is triggered by cyclic hormonal changes. The ovaries, the main source of female hormones, regulate the menstrual cycle. During menstruation, an ovum is released from an ovary and travels through the Fallopian tubes to the uterus. This journey is called ovulation. The menstrual cycle ends with the shedding of the uterus’ inner lining (unless pregnancy occurs, in which a fertilized egg travels to the uterus and implants in the lining). The first day of menstrual bleeding is calculated as “day one” of the menstrual cycle. The cycle length is different for every woman, but runs roughly 28 days.