Schematic depiction of the menstrual cycle. The female cycle consists of periodical changes of the endometrium and the simultaneous maturation of an oocyte in the ovary, as well as further cycle-dependent changes of the female genital, that are controled by a hormonal regulatory circuit. With the ovulation, estrogen (steroid hormone) is released (blue). Later, the corpus luteum additionally produces progesteron. The image also shows the phases of the uterus: proliferation, secretion, desquamation.
