It is synonymous with rule or period. It is a natural physiological process of women in reproductive age and females of some animals which expelled through the vagina a mature non fertilized egg. Takes place regularly every month or more exactly every 28 days. To present the fertilization of the ovum, menstruation disappears during the time of gestation.
Does the endometrial tissue, blood and other fluids expelled from the uterus through the vagina in women and some viviparous females in reproductive age, when they are not pollinated. The length of the menstrual cycle varies between species, the human is approximately 28 days, from where comes its name, is in latin mensis "month", more precisely by the lunar month (as an evolutionary mechanism, primitive women synchronising their days ferti (them with the new moon, when the males stayed at home and did not come out to hunt). Although in Greek there is a voice for 'Moon' that sounds like mena, philologists do not associate them, although they represent a common etimo from a proto Indo-European language.
Menstruation: f. phenomenon occurring approximately every month, whereby women and the female of some animals that have not been pregnant a viscous substance comprised of blood and eliminated other elements: some women suffer from severe pain in the womb during menstruation. Synonym: Menstrual period.
