<Tr> <Td_colspan="2"> In Wikidata </Td> </Tr> <P> 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 . </P> <P> Estrogens are synthesized in all vertebrates as well as some insects . Their presence in both vertebrates and insects suggests that estrogenic sex hormones have an ancient evolutionary history . The three major naturally occurring forms of estrogen in females are estrone (E1), estradiol (E2), and estriol (E3). Another type of estrogen called estetrol (E4) is produced only during pregnancy . Quantitatively, estrogens circulate at lower levels than androgens in both men and women . While estrogen levels are significantly lower in males compared to females, estrogens nevertheless also have important physiological roles in males . </P> <P> Like all steroid hormones, estrogens readily diffuse across the cell membrane . Once inside the cell, they bind to and activate estrogen receptors (ERs) which in turn modulate the expression of many genes . Additionally, estrogens bind to and activate rapid - signaling membrane estrogen receptors (mERs), such as GPER (GPR30). </P>

Is there such a thing as natural estrogen