Estradiol (E2 or 17β-estradiol) (also oestradiol) is a sex hormone. Estradiol is the predominant sex hormone present in females. It is also present in males, and at a higher level because it is being constantly produced. In females it is only produced 3 out of 30 days of the cycle. It represents the major estrogen in humans.
Estradiol has not only a critical impact on reproductive and sexual functioning, but also affects other organs including the bones.
Estradiol, like other steroids, is derived from cholesterol. After side
chain cleavage and utilizing the delta-5 pathway or the delta-4 pathway,
androstenedione is the key intermediary.
A fraction of the
androstenedione is converted to testosterone, which in turn undergoes
conversion to estradiol by an enzyme called aromatase. In an
alternative pathway, androstenedione is "aromatized" to estrone, which
is subsequently converted to estradiol.
During the reproductive years, most estradiol in women is
produced by the granulosa cells of the ovaries by the aromatization of
androstenedione (produced in the theca folliculi cells) to estrone,
followed by conversion of estrone to estradiol by 17β-hydroxysteroid
dehydrogenase. Smaller amounts of estradiol are also produced by the
adrenal cortex, and (in men), by the testes.
Estradiol is produced not only in the gonads: In both sexes,
precursor hormones, to be specific testosterone, are converted by
aromatization to estradiol. In particular, fat cells are active to
convert precursors to estradiol, and will continue to do so even after
menopause. Estradiol is also produced in the brain and in arterial
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