What is menstruation?

Explanation

In the absence of fertilisation, the corpus luteum degenerates. This causes disintegration of the endometrium leading to menstruation, this is due to deficiency of progesterone hormone. Menstruation lasts for 3-5 days. The menstrual flow results due to breakdown of endometrial lining of uterus and the blood vessels which forms liquid that comes out through the vagina.