Menstruation begins with the first day of bleeding. It usually lasts between 3 and 5 days, depending on each body. It is the phase in which the body expels the endometrium because there was no fertilization of the ovule.
In this phase the body begins to prepare for a pregnancy. For this, estrogen (a type of hormone) is responsible for thickening the endometrium, the inner layer of the uterus, for possible fertilization. At the same time, a hormone called folicestimulante (HEF) increases, which produces the growth of the ovarian follicles. Each follicle contains an ovule.
At this moment, an ovarian follicle is broken and an oocyte is released. This oocyte travels to the fallopian tube, where it will wait between 12 and 48 hours to be fertilized, otherwise it will begin to disintegrate.
After the oocyte is released, the follicles are transformed into the corpus luteum, a gland responsible for generating progesterone. When fertilization does not occur, the preparation process is interrupted with the detachment of the endometrium, and then menstruation takes place restarting the cycle.