estrogen

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estrogen

(ĕs`trəjən), any one of a group of hormoneshormone,
secretory substance carried from one gland or organ of the body via the bloodstream to more or less specific tissues, where it exerts some influence upon the metabolism of the target tissue.
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 synthesized by the reproductive organs and adrenal glandsadrenal gland
or suprarenal gland
, endocrine gland (see endocrine system) about 2 in. (5.1 cm) long situated atop each kidney. The outer yellowish layer (cortex) of the adrenal gland secretes about 30 steroid hormones, the most important of which are aldosterone and
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 in females and, in lesser quantities, in males. The estrogens cause the thickening of the lining of the uterusuterus,
in most female mammals, hollow muscular organ in which the fetus develops and from which it is delivered at the end of pregnancy. The human uterus is pear-shaped and about 3 in. (7.
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 and vagina in the early phase of the ovulatory, or menstrual, cycle (see menstruationmenstruation,
periodic flow of blood and cells from the lining of the uterus in humans and most other primates, occurring about every 28 days in women. Menstruation commences at puberty (usually between age 10 and 17).
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); in lower animals cyclical estrogen secretion also induces estrus, or "heat." The estrogens are also responsible for female secondary sex characteristics such as, in humans, pubic hair and breasts, and they affect other tissues including the genital organs, skin, hair, blood vessels, bone, and pelvic muscles.

The major estrogen secreted by the ovary is 17β-estradiol; this is converted to estrone in the blood. Estriol is the principal estrogen formed by the placenta during pregnancy. These three compounds, 17β-estradiol, estrone, and estriol, account for most of the estrogenic activity in humans.

The ability of estrogens to suppress secretion of follicle-stimulating hormone (FSH) by the pituitary glandpituitary gland,
small oval endocrine gland that lies at the base of the brain. It is sometimes called the master gland of the body because all the other endocrine glands depend on its secretions for stimulation (see endocrine system).
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 and thereby inhibit ovulation makes estrogen and estrogenlike compounds major components in oral contraceptives. Estrogen replacement therapy (ERT) uses synthetic estrogen (e.g., Premarin), typically given with progestins (e.g., Provera) to treat the physical changes of menopausemenopause
or climacteric
, transitional phase in a woman's life when the ovaries stop releasing eggs, ovarian production of estrogen and other hormones tapers off, and menstruation ceases.
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, including hot flashes and vaginal dryness. ERT also retards the development of osteoporosisosteoporosis
, disorder in which the normal replenishment of old bone tissue is severely disrupted, resulting in weakened bones and increased risk of fracture; osteopenia results when bone-mass loss is significant but not as severe as in osteoporosis.
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 in postmenopausal women but increases the risk of breast cancerbreast cancer,
cancer that originates in the breast. Breast cancer is the second leading cause of cancer death in women (following lung cancer). Although the vast majority of the cases occur in women, some men also get breast cancer.
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, heart attack (see infarctioninfarction,
blockage of blood circulation to a localized area or organ of the body resulting in tissue death. Infarctions commonly occur in the spleen, kidney, lungs, brain, and heart.
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), strokestroke,
destruction of brain tissue as a result of intracerebral hemorrhage or infarction caused by thrombosis (clotting) or embolus (obstruction in a blood vessel caused by clotted blood or other foreign matter circulating in the bloodstream); formerly called apoplexy.
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, and, when not given with progestins, uterine cancer. Estrogens are also used to treat prostate cancer.

Estrogen

A substance that maintains the secondary sex characters and organs, such as mammary glands, uterus, vagina, and fallopian tubes, of mammalian females. Naturally occurring substances with this activity are steroid hormones. The principal estrogenic hormone substances are 17(ß)-estradiol (with the structure shown), estrone, and estriol. They are produced and secreted directly into the bloodstream by the ovary, testis, adrenal, and placenta of pregnancy. Two other naturally occurring estrogenic hormones, equilin and equilenin, have been obtained only from the urine of pregnant mares and are apparently peculiar to that species. Stilbestrol, a synthetic compound with considerable estrogenic activity, has been used extensively in medical practice. See Hormone, Steroid

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Estrogen

 

any of a number of female sex hormones (including estradiol, estriol, and estrone) produced mainly by the ovarian follicles and placenta and to some extent by the adrenal cortex and testes.

Steroids in chemical structure, estrogens stimulate the growth and development of the genitalia and secondary sex characteristics in women and in the females of many mammals. Estrogens contain 18 carbon atoms and possess the chemical properties of phenols. The biosynthesis of these steroid hormones in mammals is one of the final stages in the metabolism of cholesterol. The closest biogenetic precursors of estrogens are androgens (male sex hormones).

Estrogens occur in the blood in complexes with proteins and are found in concentrations of less than 10 micrograms/liter (μg/l) in both men and women. Estrogens are excreted from the body together with urine. In males estrogens are excreted evenly, but in females the process has two peaks—during ovulation and at the time of maximum activity of the yoke sac. During pregnancy and especially toward the end of the term, the level of estrogens in women’s blood rises to 70–80 μg/l as a result of the marked intensification of the biosynthesis of the hormone in the placenta. Estrogens cause thickening of the epithelium of the vaginal mucosa, an increase in the weight of the uterus, the rhythmic contraction of the uterus, stimulation of the alveolar tissue of the breasts, formation of a layer of subcutaneous fat, the growth of hair of the female type, and a persistent sex drive. Together with the hormone progesterone, they facilitate the implantation of the fertilized egg, help maintain pregnancy, and ease childbirth. Estrogens play an important role in the regulation of many other biochemical processes by participating in the metabolism of carbohydrates and the distribution of lipids, stimulating the synthesis of amino acids, nucleic acids, and proteins, aiding the deposition of calcium in bone tissue, and delaying the excretion of sodium, inorganic phosphorus, and water.

The secretion of estrogens is controlled by the anterior pituitary and its gonadotropic hormones—the follicle-stimulating hormone (FSH) and the luteinizing hormone (LH). The biochemical mechanism of the action of steroid hormones is probably related to the stimulation of the synthesis of ribonucleic acid (RNA) in the cells and tissues of the reproductive organs, which causes a change in the rate and volume of protein biosynthesis (seeTRANSLATION).

Synthetic steroid derivatives of estrogens (including estradiol dipropionate, estradiol benzoate, and ethinyl estradiol) are used to treat such problems as hyperplasia of the genitalia in women, disturbances of the menstrual cycle, climacteric disorders, and certain diseases affecting the sexual organs in female mammals. Considerable estrogenic activity is also exhibited by such other compounds as synthetic nonsteroid derivatives of 1,2-diphenyl-ethylene, including diethylstilbestrol, hexestrol, and synestrol; of triphenylethylene, including chlorotrianisene and bromotriphenylethylene; and of α-naphthylpropionic acid, including allenoic acid and 3-(5-naphthol)-4,4-dimethylpentanoic acid.

Estrogens are found not only in humans and animals but also in some higher plants, especially in certain flowers (such as the flower of the willow) and fruits (such as apples, coconuts, dates, and pomegranates), but their function and metabolism is still obscure. Such microorganisms as Nocardia restricta and Septomyxa offinis can also synthesize estrogens from sterols. Many legumes, including clover, soya, and alfalfa, form oxygen-containing heterocyclic compounds with high estrogenic activity; such compounds include coumestrol, genistein, and mirestrol.

REFERENCES

Pfizer, L., and M. Pfizer. Steroidy. Moscow, 1964. (Translated from English.)
Heftman, E. Biokhimiia steroidov. Moscow, 1972. (Translated from English.)

E. P. SEREBRIAKOV

estrogen

[′es·trə·jən]
(biochemistry)
Any of various natural or synthetic substances possessing the biologic activity of estrus-producing hormones.

oestrogen

(US), estrogen
any of several steroid hormones, that are secreted chiefly by the ovaries and placenta, that induce oestrus, stimulate changes in the female reproductive organs during the oestrous cycle, and promote development of female secondary sexual characteristics
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