Estrogen is one of a group of
steroid hormones that control female sexual development, both promoting
and function of the female sex organs, and also the female secondary
sexual characteristics - including breast development, for example.
Although estrogens are synthesized mainly by the ovaries, some small
quantities of estrogen are also produced by the adrenal
and the placenta.
(Estrogen is present in males, but excessive production of estrogen in men
can lead to feminization.)
The actions of the hormone estrogen include: