Question

why does menstruation occur?

Answer 1

The menstrual cycle occurs due to the rise and fall of hormones. This cycle results in the thickening of the lining of the uterus, and the growth of an egg, (which is required for pregnancy). ... If pregnancy does not occur, the lining is released in what is known asmenstruation.

Answer 2

The ovary of a woman release one egg every month therefore, the uterus also prepares itself every month to receive a fertilised egg. In this process the uterus wall becomes thick and soft with lots of blood capillaries in it. In case the egg is fertilised by a sperm then uterus has keep this fertilised egg and nourish it and develop into a baby. If however, the egg released by the ovary but not fertilised then thick lining of uterus wall is broken and comes out vagina in the form of blood