gonadotropic hormone


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Related to gonadotropic hormone: adrenocorticotropic hormone

gonadotropic hormone

(gō'nădətrŏp`ĭk) or

gonadotropin,

any one of three glycoprotein (see proteinprotein,
any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight.
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) 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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 released by either the anterior 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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 or the placenta (the organ in which maternal and fetal blood exchange nutrients and waste products) that have various effects upon the ovariesovary,
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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 and testes (see testistestis
or testicle
, one of a pair of glands that produce the male reproductive cells, or sperm. In fetal life the testes develop in the abdomen, then descend into an external sac, the scrotum.
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). Gonadotropin-releasing hormone (Gn-RH) is produced and released from the hypothalamus. Gn-RH release stimulates the secretion of both follicle-stimulating hormone (FSH) and lutenizing hormone (LH) from the pituitary gland. Gn-RH is a peptide composed of ten amino acids which are synthesized in the hypothalamus (that portion of the brain nearest the pituitary). This hormone travels in the bloodstream to the anterior pituitary, where it causes the release of the gonadotropic hormones. The hormones FSH and LH inhibit the amount of Gn-RH released by a mechanism called "negative feedback." In the female, FSH causes an increase in the weight of the ovaries and encourages the growth of Graafian follicles (containing maturing eggs); in males, FSH produces spermatogenesis in the testes. In females, secretion of LH is associated with the maturation of the follicles, the manifestation of heat (or estrus), and the release of the egg from the follicle, which is transformed into a corpus luteum. In males, LH stimulates the testes to release testosterone. Sex hormones released from the ovaries and testes eventually reach the hypothalamus and help to regulate the hormonal cycle. Human chorionic gonadotropin (HCG), produced in the placenta, helps to maintain pregnancy once a fetus begins to develop. It appears in the urine in approximately the first week after the first missed menstrual period, and is the basis for two kinds of pregnancy tests; in the Ascheim-Zondek testm it causes the ovaries of an immature female rat or mouse to gain weight and produce ripened follicles, and in the Friedman test, it stimulates female rabbits to ovulate.

gonadotropic hormone

[gō¦nad·ə¦träp·ik ′hȯr‚mōn]
(biochemistry)
Either of two adenohypophyseal hormones, FSH (follicle-stimulating hormone) or ICSH (interstitial-cell-stimulating hormone), that act to stimulate the gonads.