Shown here is a schematic representation of the menstrual cycle. The menstrual cycle refers to the periodic changes of the endometrium and the synchronous maturation of an egg cell in the ovary and other cycle-dependent changes in the female genitalia that are controlled by a hormonal loop. With the expulsion of the oocyte a bolus of estrogen (steroid hormone) is released (blue). Later, progesteron is produced by the corpus luteum. Furthermore one can see the proliferative, secretory and desquamation-phase of the uterus.