Estrogen is actually a broad term referring to several different forms. The 3 main estrogens are known as E1, E2 and E3. The proper name for E1 is Estrone. This is a very strong form of estrogen and usually the one that becomes dominant in later life because the body continues to produce it. Estradiol is known as E2 and is also a very strong estrogen. However, it can become deficient in later life and you can experience symptoms and could possibly need to supplement it. E3 is Estriol (known as the gentle estrogen) Estriol is a very protective form of estrogen and is the estrogen most dominant during pregnancy because of its ability to protect the fetus.
A chemical substance secreted by an endocrine gland or group of endocrine cells that acts to control or regulate specific physiological processes, including growth, metabolism, and reproduction. Most hormones are secreted by endocrine cells in one part of the body and then transported by the blood to their target site of action in another part, though some hormones act only in the region in which they are secreted. Many of the principal hormones of vertebrates, such as growth hormone and thyrotropin, are secreted by the pituitary gland, which is in turn regulated by neurohormone secretions of the hypothalamus. Hormones also include the endorphins, androgens, and estrogens. See more at endocrine gland .