What is menstruation? Explain.

Menstruation is a phenomenon of blood flow which related to the reproductive acitivity start in women. In a female, the reproductive organs are called ovaries. This blood flow is started when the female reproductive cell called ovum, matures and is released by one of the ovaries once in about 28 to 30 days. During this period, the wall of the uterus becomes thick so as to receive the egg, in case it is fertilized and begins to develop. If fertilization does not occur, the released ovum and the thickened lining of the uterus along with its blood vessels are shed off from the reproductive organ i.e. vagina. Menstruation lasts for the period of 4 to 5 days.