Estrogen , or oestrogen , is the primary female sex hormone. It is responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens in females that have estrogenic hormonal activity: estrone , estradiol , and estriol. The estrane steroid estradiol is the most potent and prevalent of these. Estrogens are synthesized in all vertebrates  as well as some insects. The three major naturally occurring forms of estrogen in women are estrone E1 , estradiol E2 , and estriol E3.
Estrogen and Testosterone Hormones
Secondary sex characteristic - Wikipedia
Estrogens are a group of hormones that are essential for the sexual and reproductive development in women. They are the primary female sex hormones. Estrogens are mainly produced by a woman's ovaries, but the adrenal glands also produce a small quantity of this hormone. They play an important role in the regulation of the menstrual cycle, but also affect the heart, blood vessels, bones, breasts, skin, hair, mucous membranes, pelvic muscles, and the brain. Similar to estrogen, progesterone is also a female sex hormone and is vital for the regulation of various bodily functions.
What to know about female sex hormones
Gonads are the male and female primary reproductive organs. The male gonads are the testes and the female gonads are the ovaries. As a component of the endocrine system , both male and female gonads produce sex hormones. Male and female sex hormones are steroid hormones and as such, can pass through the cell membrane of their target cells to influence gene expression within cells.
The human reproductive system allows for the production of offspring and the continuation of the species. Males and females have distinct reproductive organs and glands which form gametes sperm in males, eggs, or ova , in females which unite to form the embryo. The reproductive system is controlled by chemicals called hormones.