Estrogen
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Estrogens (or oestrogens) are a group of steroid compounds that function as the primary female sex hormone. They are produced primarily by developing follicles in the ovaries, the corpus luteum and the placenta. Some estrogens are also produced in smaller amounts by other tissues such as liver, adrenal glands and the breasts. These secondary sources of estrogen are especially important in post-menopausal women.
Synthesis of oestrogenes starts in theca interna cells in the ovary, by the synthesis of androstenedione from cholesterol. Androstenedione is a substance of moderate androgenic activity. This compound crosses the basal membrane into the surrounding granulosa cells cells, where it is converted to estrone or estradiol, either immediately or through testosterone. Presence of both cell types is essential for estrogen synthesis.
The three naturally occurring estrogens are estradiol, estriol and estrone. In the body these are all produced from androgens through enzyme action. Estradiol is produced from testosterone and estrone from androstenedione. Estrone is weaker than estradiol, and in post-menopausal women more estrone is present than estradiol.
While estrogens are present in both men and women, they are found in women in significantly higher quantities. They promote the development of female secondary sexual characteristics, such as breasts, and are also involved in controlling the menstrual cycle, which is why most oral contraceptives contain estrogens.
The use of estrogen, especially together with progesterone, is a controversial treatment for the symptoms of menopause which may do as much harm as good.
Estrogenic compounds
A range of other synthetic and natural substances have been identified that possess estrogenic activity. These include bisphenol-A, phthalate esters and nonylphenol.
See also
de:Östrogen es:Estrógeno fr:Estrogène nl:Oestrogeen ja:エストロゲン pl:Estrogeny sv:Östrogen