Female sex hormone. Polarised light micrograph of crystals of estrone. Estrone is one of the six naturally-occurring estrogens, a class of hormones associated with the development of female reproductive organs and secondary sex characteristics. Estrone is secreted mainly in the ovaries, and is made by the action of enzymes on pregnenolone. Estrone sulphate may be used in hormone replacement therapy to treat some clinical symptoms of the menopause. Magnification x10 at 35mm size.