Why does menstruation occur?

In every ovulation cycle, an egg is discharged from the ovary which is exchanged to the fallopian tube. Also, the uterus sets itself up for a conceivable pregnancy. The lining of uterus thickens. At the point when no conception happens, the covering of the uterus is shed in pieces; alongside the unfertilized egg. These things are discharged out through the vagina through dying; called mensuration. The sole reason for the mensuration to occur is due the change in the levels of female hormones, oestrogen and progesterone.