menstruation /men′stro̅o̅·ā″shən/ [L, menstruare, to menstruate] , the periodic discharge through the vagina of a bloody secretion containing tissue debris from the shedding of the endometrium from the nonpregnant uterus. The average duration of menstruation is 4 to 5 days, and it recurs at approximately 28-day intervals throughout the reproductive life of nonpregnant women. Kinds include anovular menstruation, retrograde menstruation, vicarious menstruation. See also menstrual cycle. −menstruate, v.
