Menstruation is a very common phenomenon appears to females.

It starts from 12-13yr. Sometimes may be due to some reason thears a delay in its starting. The appearance of it at 1st time is called menarche.

Menstrual cycle occurs in a 28 day cyclic manners. In this cycle 1st 1-4/5 day is menstrual phage. During this menstruation occurs. & at this time break down of endometrium leads to a cause of menstrual blood flow. Due to lack of estrogen & some other hormones it happens.

Now...