In female, ovaries release ovum or egg once every 28 days from the age of puberty. The uterus prepares itself every month to receive a fertilized egg. Thus, its lining becomes thick and spongy. If the egg is not fertilized it lives for about one day. Afterwards this lining of uterus is no longer required and menstruation occurs.

Menstrual is the time of uterine bleeding in which an unfertilized egg and the thick uterine lining. It occurs through the vagina as blood and mucus.