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.