progesterone


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progesterone

(prōjĕs`tərōn'), female sex hormonehormone,
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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 that induces secretory changes in 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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 essential for successful implantation of a fertilized egg. A steroidsteroids,
class of lipids having a particular molecular ring structure called the cyclopentanoperhydro-phenanthrene ring system. Steroids differ from one another in the structure of various side chains and additional rings. Steroids are common in both plants and animals.
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, progesterone is secreted chiefly by the corpus luteum, a group of cells formed in the ovaryovary,
ductless gland of the female in which the ova (female reproductive cells) are produced. In vertebrate animals the ovary also secretes the sex hormones estrogen and progesterone, which control the development of the sexual organs and the secondary sexual characteristics.
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 after the follicle ruptures during the release of the egg cell. If fertilization does not take place, the secretion of progesterone decreases and menstruation occurs. If fertilization does occur, progesterone is secreted during pregnancy by the placenta and acts to prevent spontaneous abortion; the hormone also prepares the mammary glands for milk production. Progesterone is also synthesized from cholesterolcholesterol
, fatty lipid found in the body tissues and blood plasma of vertebrates; it is only sparingly soluble in water, but much more soluble in some organic solvents. A steroid, cholesterol can be found in large concentrations in the brain, spinal cord, and liver.
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 in the cortex of the adrenal glandadrenal 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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 where it is a precursor for the synthesis of other steroids including testosteronetestosterone
, principal androgen, or male sex hormone. One of the group of compounds known as anabolic steroids, testosterone is secreted by the testes (see testis) but is also synthesized in small quantities in the ovaries, cortices of the adrenal glands, and placenta, usually
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. Synthetic compounds with progesteronelike activity have been developed that, along with estrogenestrogen
, any one of a group of hormones synthesized by the reproductive organs and adrenal glands in females and, in lesser quantities, in males. The estrogens cause the thickening of the lining of the uterus and vagina in the early phase of the ovulatory, or menstrual, cycle
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, are used in oral contraceptives.

Progesterone

A steroid hormone produced in the corpus luteum and placenta. The hormone has an important physiological role in the luteal phase of the menstrual cycle and in the maintenance of pregnancy. In addition, progesterone produced in the testis and adrenals has a key role as an intermediate in the biosynthesis of androgens, estrogens, and the corticoids (adrenal cortex steroids). See Androgen, Cholesterol, Estrogen, Menstruation, Steroid, Sterol

Progesterone

 

in humans and vertebrate animals, a female sex hormone. Chemically, progesterone is a steroid that is synthesized in the body from cholesterol. It is an intermediate in the biosynthesis of all steroid hormones and can form in any tissues that secrete these hormones. Its structural formula is

In humans and higher animals, progesterone is primarily synthesized in the corpus luteum of the ovaries; the luteinizing hormone of the pituitary gland regulates its production. In the blood, progesterone mainly occurs in complexes with proteins.

By interacting with estriadol, another female hormone, progesterone regulates the estrous cycle in mammals and the menstrual cycle in humans. In the preovulatory phase of the sex and reproductive cycles in women, the daily production of progesterone occurs principally in the adrenal cortex and measures 1 to 3 mg. In the postovulatory phase, as much as 20 to 30 mg of progesterone are produced, principally in the corpus luteum. Progesterone produces changes in the uterine mucosa, which prepare the uterus for the implantation of the fertilized egg. When fertilization does not occur, the corpus luteum atrophies and the secretion of progesterone decreases. During a normal pregnancy, the placenta participates in the required daily production of as much as 200 to 250 mg of progesterone. Progesterone suppresses the activity of the smooth musculature of the uterus and thus prevents spontaneous abortion of the fetus; it also inhibits the ovulation of new follicles. The concentration of progesterone in the uterus decreases at the end of pregnancy, which serves as one of the trigger mechanisms of childbirth.

In medicine, progesterone and its synthetic derivatives (generally called progestins, or gestagens) are used to treat various disturbances of pregnancy and the ovarian cycle; they are also used in combination with estrogens as contraceptives. Derivatives of progesterone that act as repellents have been discovered in some insects. Flowering plants have also been found to produce progesterone.

In 1934, A. Butenandt contributed to the discovery of the chemical structure of progesterone.

REFERENCES

Savchenko, O. N. Gormony iaichnika i gonadotropnye gormony. Leningrad, 1967.
Heftmann, E. M. Biokhimiia steroidov. Moscow, 1972. (Translated from English.)

B. V. POKROVSKII

progesterone

[prō′jes·tə‚rōn]
(biochemistry)
C21H30O2 A steroid hormone produced in the corpus luteum, placenta, testes, and adrenals; plays an important physiological role in the luteal phase of the menstrual cycle and in the maintenance of pregnancy; it is an intermediate in the biosynthesis of androgens, estrogens, and the corticoids.

progesterone

a steroid hormone, secreted mainly by the corpus luteum in the ovary, that prepares and maintains the uterus for pregnancy. Formula: C21H30O2
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