Women without ovaries do not have menstruation. The blood of menstruation comes from the endometrium, which is shed by the uterine lining, but the shedding of the endometrium is affected by the cyclical changes of the ovaries. Menstruation is the periodic shedding of the endometrium and bleeding that occurs along with the cyclical changes of the ovaries. From this definition, it can be seen that the shedding and bleeding of the endometrium requires the cyclic changes of estrogen and progesterone secreted by the ovaries. Usually on the fifth day of menstruation, this is when the endometrium begins to proliferate, mainly due to the influence of follicular development in the ovaries, which results in an increase in estrogen, leading to the proliferation of the endometrium. After the endometrium has proliferated to a certain extent, the follicles develop to their maximum size, and at this time the eggs are discharged and the corpus luteum is formed. The corpus luteum in turn secretes progesterone and a small amount of estrogen. The estrogen and progesterone secreted by the corpus luteum then cause the endometrium to change during the secretory phase, so the endometrium will continue to thicken. When the corpus luteum reaches its maximum volume, at this time, if the sperm and egg are not fertilized, the corpus luteum will shrink and the endometrium will experience periodic exfoliation and bleeding. As you can see, menstruation must be accompanied by changes in ovarian hormones in order to be produced.