I here have seen sobshchenie Annas, and in passing would like to learn or find out, about a menses, that...

[Ira]

I here have seen sobshchenie Annas, and in passing would like to learn or find out, about a menses, what is it such, why, and what for.

[Pasenjuk A.M.]

Menses this casting-off of an internal layer of a uterus under action of hormones. It is necessary for prevention of growth endometrija if there was no fertilization. More in detail - "human physiology" or to the teacher of biology.