estrogen
Meaning of estrogen: After menopause the ovaries largely stop making it, and fat tissue converting adrenal hormones becomes the main remaining source.
Definition of estrogen
Estrogen is a group of closely related steroid hormones that drive female sexual development and regulate the menstrual cycle, the lining of the uterus and the upkeep of bone. The ovaries are the main source during the reproductive years, with smaller amounts made elsewhere, and men produce and depend on estrogen too, in far lower quantities.
What are the three main forms?
| Form | When it predominates |
|---|---|
| Estradiol | The most potent form and the main one between puberty and menopause |
| Estrone | Weaker, and the chief circulating form after menopause |
| Estriol | Weakest of the three, produced in large amounts by the placenta during pregnancy |
Where the supply comes from shifts along with which form dominates. Before menopause the ovaries make most of it directly. Afterward they largely stop, and what remains is produced by converting androgens from the adrenal glands into estrone, a reaction carried out by an enzyme called aromatase in fat, muscle and skin. That is why body fat influences estrogen levels more after menopause than before, and why drugs blocking aromatase lower estrogen effectively in that setting but not in a woman whose ovaries are still active.
What does it actually do?
Estrogen enters cells and binds an estrogen receptor, which then switches particular genes on or off. Those receptors sit in many tissues, so its reach is wide. At puberty it drives breast development and growth of the uterus and vagina and shapes the distribution of body fat. Through the reproductive years it thickens the uterine lining in the first half of each cycle and triggers the surge that releases an egg. It restrains the cells that break down bone, so falling levels after menopause speed bone loss and raise the risk of osteoporosis. It also closes the growth plates at the ends of the long bones in both sexes, setting final adult height, and it affects cholesterol handling, blood clotting, skin, and the lining of the vagina and urethra.
How is it given, and why is it blocked?
Manufactured estrogen is used in hormonal contraception, in treating menopausal symptoms, in certain menstrual disorders and in gender affirming care. Blocking it matters just as much. Many breast cancers grow in response to estrogen, so treatment for those tumors works either by occupying the receptor so the hormone cannot reach it or by shutting production down, which is the reason a tumor is tested for receptor status before hormone treatment is considered. Estrogen given on its own raises the risk of cancer of the uterine lining in anyone who still has a uterus, so a progestogen is normally given alongside it, and estrogen also raises the risk of clots in the veins.
Also known as
Used in a sentence
Estrogen levels were measured as part of the evaluation for the patient's irregular menstrual cycles.
Good to know
Estrogen is often spoken of as a single hormone, though the term covers several molecules whose relative amounts shift across life, so a laboratory result depends on which form was measured and at what point in the cycle the sample was taken.
Word origin
Where “estrogen” comes from
Coined from estrus, from Greek oistros, meaning frenzy or gadfly, an early term for the reproductive cycle, combined with -gen, from Greek gennan, meaning to produce.