estrogen
n. any of a class of steroid hormones that are produced mainly by the ovaries and act as the principal female sex hormones, inducing estrus in female mammals and secondary female sexual characteristics in humans. The estrogens occurring naturally in humans are estradiol, estrone, and estriol, secreted by the ovarian follicle, corpus luteum, placenta, testes, and adrenal cortex. Estrogens are also produced by certain plants; these phytoestrogens may be used in the manufacture of synthetic steroid hormones. Estrogens are used therapeutically in estrogen replacement therapy and oral contraceptives and to treat certain menstrual disorders and some types of breast and prostate cancers.