hormone

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hormone

hormone, 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. Normally, various hormones are produced and secreted by the endocrine glands (see endocrine system), including the pituitary, thyroid, parathyroids, adrenals, ovaries, testes, pancreatic islets, certain portions of the gastrointestinal tract, and the placenta, among the mammalian species. As lack of any one of them may cause serious disorders, many hormones are now produced synthetically and used in treatment where a deficiency exists. The hormones of the anterior pituitary include thyrotropin, adrenocorticotropic hormone, the gonadotropic hormones, and growth hormone; the posterior pituitary secretes antidiuretic hormone, prolactin, and oxytocin. The thyroids secrete thyroxine and calcitonin, and the parathyroids secrete parathyroid hormone. The adrenal medulla secretes epinephrine and norepinephrine while the cortex of the same gland releases aldosterone, corticosterone, cortisol, and cortisone. The ovaries primarily secrete estrogen and progesterone and the testes testosterone. The adrenal cortex, ovaries, and testes in fact produce at least small amounts of all of the steroid hormones. The islets of Langerhans in the pancreas secrete insulin, glucagon, and somatostatin. The kidneys also produce erythropoietin, which produces erythrocytes (red blood cells). The passage of chyme (see digestive system) from the stomach to the duodenum causes the latter to release secretin, which stimulates the flow of pancreatic juice. The duodenum can also be stimulated by the presence of fats in the chyme to secrete cholecystokinin, a hormone that stimulates the gall bladder to contract and release bile. There is evidence that the upper intestine secretes pancreatozymin, which enhances the amount of digestive enzymes in the pancreatic juice. In addition, the pyloric region of the stomach secretes gastrin, a hormone that increases the secretion of hydrochloric acid into the stomach. The placenta has been shown to secrete progesterone and chorionic gonadotropin. There is evidence that it even contains a substance similar to growth hormone. Insects have a unique hormonal system that includes ecdysone, a steroid that influences molting and metamorphosis, and juvenile hormone, needed for early development. Plants, too, have a hormonal system, which includes the auxins, the gibberellins, the cytokinins, and substances associated with the formation of flowers, tubers, bulbs, and buds. Ethylene is said to function as a hormone in plants, acting to hasten the ripening of fruits.
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Hormone

One of the chemical messengers produced by endocrine glands, whose secretions are liberated directly into the bloodstream and transported to a distant part or parts of the body, where they exert a specific effect for the benefit of the body as a whole. The endocrine glands involved in the maintenance of normal body conditions are pituitary, thyroid, parathyroid, adrenal, pancreas, ovary, and testis. However, these organs are not the only tissues concerned in the hormonal regulation of body processes. For example, the duodenal mucosa, which is not organized as an endocrine gland, elaborates a substance called secretin which stimulates the pancreas to produce its digestive juices. The placenta is also a very important hormone-producing tissue. See separate articles on the individual glands.

The hormones obtained from extracts of the endocrine glands may be classified into four groups according to their chemical constitution: (1) phenol derivatives, such as epinephrine, norepinephrine, thyroxine, and triiodothyronine; (2) proteins, such as the anterior pituitary hormones, with the exception of adrenocorticotropic hormone (ACTH), human chorionic gonadotropin, pregnant-mare-serum gonadotropin, and thyroglobulin; (3) peptides, such as insulin, glucagon, ACTH, vasopressin, oxytocin, and secretin; and (4) steroids, such as estrogens, androgens, progesterone, and corticoids. Hormones, with a few exceptions like pituitary growth hormone and insulin, may also be classified as either tropic hormones or target-organ hormones. The former work indirectly through the organs or glands which they stimulate, whereas the latter exert a direct effect on peripheral tissues. See Endocrine system (vertebrate)

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

hormone

[′hȯr‚mōn]
(biochemistry)
A chemical messenger produced by endocrine glands and secreted directly into the bloodstream to exert a specific effect on a distant part of the body.
An organic compound that is synthesized in minute quantities in one part of a plant and translocated to another part, where it influences a specific physiological process.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

hormone

1. a chemical substance produced in an endocrine gland and transported in the blood to a certain tissue, on which it exerts a specific effect
2. an organic compound produced by a plant that is essential for growth
3. any synthetic substance having the same effects
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Dioxin's new target Scientists found indications that dioxin, a hormonelike pollutant, can trigger breast cancer in heavily exposed women (162: 77).
Gonadotropins are hormonelike agents released by the pituitary (LH - luteinizing hormone, and FSH - follicle stimulating hormone).
Similarly, hormonelike signaling has also been observed when vertebrates are exposed to plant chemicals called phytoestrogens.
For example, natural hormonelike compounds called prostaglandins influence blood pressure, inflammation, and muscle contraction.
IL-15, like IL-6, is hormonelike in action when released in the context of exercise.
More subtle effects on the endocrine system and menstrual cycling from consumption of foods containing hormonelike substances have also been suggested (Cassidy et al.
Some hormones, for example, cause the greatest effects at low and high doses, with little effect at intermediate exposures, This dose-response pattern, known as a U-shaped curve, has also been seen with hormonelike pollutants.
Comment: EFAs are precursors to prostaglandins, a group of hormonelike compounds that were so named because of their presence in high concentrations in prostatic secretions.
Researchers have shown that, on the biochemical level, Cox-2 chemically alters prostaglandin, a hormonelike compound that stimulates inflammation and cell proliferation.
The ranking of estrogenic potency in the T47D.Luc cells of the thyroid hormonelike HO-PBDEs was [T.sub.2]-like HO-BDE ([EC.sub.50], 0.1 [micro]M) [is greater than] [T.sub.3]-like HO-BDE ([EC.sub.50], 0.5 [micro]M) >>> [T.sub.4]-like HO-BDE.
In addition, lactate has several other surprising actions that have led several researchers to refer to it as a "lactormone," since it seems to have hormonelike action as a signaling molecule.
When physicians administered the hormonelike drug prostaglandin to induce labor, the rate of ruptures soared to 24.5 ruptures per 1,000 deliveries.