Any of a class of hormones that primarily influence the female
The three major estrogens
estradiol, estrone, and estriol
are produced mainly by the ovaries and {{link=placenta">placenta ; the adrenal gland s and the testes secrete smaller amounts. Estrogens affect the ovaries, vagina , fallopian tubes, uterus , and mammary gland s and play crucial roles in puberty , menstruation , pregnancy , and parturition (labour). They also influence the structural differences between female and male bodies. In experimental animals, loss of estrogens diminishes mating desires and other behavioral patterns.