In human females, an unfertilized egg survives for approximately one day. The ovary releases an egg monthly, prompting the uterus to prepare for a potential fertilized egg by thickening and spongifying its lining. This lining would support embryo nourishment if fertilization occurred. If fertilization does not happen, this thickened lining is no longer needed. Consequently, it breaks down and is expelled from the body through the vagina as blood and mucus. This cyclical process occurs roughly every month and is called menstruation.