Menstruation is part of the menstrual cycle, which helps a woman's body prepare for the possibility of pregnancy each month. A cycle starts on the first day of a period. The average menstrual cycle is 28 days long. However, a cycle can range anywhere from 23 days to 35 days...The parts of the body involved in the menstrual cycle include the brain, pituitary gland, uterus and cervix, ovaries, fallopian tubes, and vagina.
