Estrogen and progesterone

Estrogen and progesterone are the female sex hormones, and they’re produced mainly by the ovaries - the female gonads.

The female body can synthesize 3 types of estrogens: estradiol, estrone and estriol.

Of the three, the ovaries synthesize estradiol, which is the most biologically active of them all, and accounts for the majority of sex-specific changes that begin in puberty - like monthly ovulation and menstruation as well as the development of the secondary sex characteristics.

Small amounts of estrogen are also produced by the adrenal cortex and fat cells in adipose tissue, and the placenta secretes these hormones during pregnancy, as well.

But during the reproductive period, it’s the ovaries that produce the majority of estrogen and progesterone in the female body.

Before puberty, the hypothalamus secretes small amounts of a hormone called gonadotropin-releasing hormone, or GnRH.

That GnRH travels to the nearby pituitary, which secretes two hormones of its own - follicle stimulating hormone, or FSH, and luteinizing hormone, or LH.

Once puberty hits, the hypothalamus starts to secrete GnRH in pulses, sometimes more and sometimes less, and FSH and LH make the ovarian follicles develop and secrete hormones.

The ovarian follicles are scattered throughout the ovaries, and each ovarian follicle is made up of a ring of follicular cells surrounding a primary oocyte at its core.