The estrogenic hormones are uniquely responsible for the growth and development of female sexual characteristics and reproduction in both humans and animals. The term "estrogen" includes a group of chemically similar hormones: estrone, estradiol (the most abundant) and estriol. Overall, estrogen is produced in the ovaries, adrenal glands and fat tissues. More specifically, the estradiol and estrone forms are produced in the ovaries, while estriol is produced by the placenta during pregnancy.
In women, estrogen circulates in the bloodstream and binds to estrogen receptors on cells in targeted tissues, affecting not only the breast and uterus, but also the brain, bone, liver, heart and other tissues.
Estrogen controls growth of the uterine lining during the first part of the menstrual cycle, causes changes in the breasts during adolescence and pregnancy, and regulates various other metabolic processes, including bone growth and cholesterol levels.
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