hormone
[hor´mōn] a chemical transmitter substance produced by cells of the body and transported by the bloodstream to the cells and organs on which it has a specific regulatory effect. adj.,
adj hormo´nal. Hormones act as chemical messengers to body organs, stimulating certain life processes and retarding others. Growth, reproduction, control of metabolic processes, sexual attributes, and even mental conditions and personality traits are dependent on hormones.
Hormones are produced by various organs and body tissues, but mainly by the
endocrine glands, such as the pituitary, thyroid, and gonads (testes and ovaries). Each gland apparently synthesizes several kinds of hormones; the adrenal glands alone produce more than 25 varieties. The total number of hormones is still unknown, but each has its unique function and its own chemical formula. After a hormone is discharged by its parent gland into the capillaries or the lymph, it may travel a circuitous path through the bloodstream to exert influence on cells, tissues, and organs (target organs) far removed from its site of origin.
One of the best-known endocrine hormones is
insulin, a protein manufactured by the beta cells of the islands of Langerhans in the pancreas that is important in carbohydrate metabolism. Other important hormones are
thyroxine, an iodine-carrying amino acid produced by the thyroid gland;
cortisone, a member of the steroid family from the adrenal glands; and the sex hormones,
estrogen from the ovaries and
androgen from the testes. Certain hormone substances can be synthesized in the laboratory for treatment of human disease. Animal hormones can also be used, as endocrine hormones are to some extent interchangeable among species. Extracts from the pancreas of cattle, for example, enabled diabetes sufferers to live normal lives even before the chemistry of insulin was fully understood.
Endocrine hormone synthesis and secretion is controlled and regulated by a closed-loop system. Negative
feedback loops maintain optimal levels of each hormone in the body. If there are abnormally high levels of a hormone in the blood, feedback to the gland responsible for its production inhibits secretion. If there are abnormally low levels, the gland is stimulated to step up production and secretion. In this way a homeostatic balance is maintained. (See also
endocrine glands.)
adrenocortical hormone 1. any of the corticosteroids secreted by the
adrenal cortex, the major ones being the glucocorticoids and mineralocorticoids, and including some androgens, progesterone, and estrogens.
corticotropin-releasing hormone (CRH) a neuropeptide secreted by the median eminence of the hypothalamus that binds to specific receptors on the corticotroph cells of the anterior pituitary and stimulates the secretion of
corticotropin.
ectopic h's those secreted by tumors of nonendocrine tissues but having the same physiologic effects as their normally produced counterparts. It is not known exactly how the synthesis and secretion of endocrine hormones from nonendocrine tissues occurs. Most of these tumors are derived from tissues that have a common embryonic origin with endocrine tissues. When the cells undergo neoplastic transformation, they can revert to a more primitive stage of development and begin to synthesize hormones.
Ectopic hormones present serious problems for patients and add to the complexity of caring for those with certain kinds of neoplastic diseases. These hormones do not respond to the feedback mechanisms that regulate normal hormonal production; hence, surgery and destruction of the tumorous tissue by radiation and chemotherapy are the treatments of choice.
follicle-stimulating hormone (FSH) one of the
gonadotropins of the anterior pituitary, which stimulates the growth and maturity of graafian follicles in the ovary, and stimulates spermatogenesis in the male.
growth hormone–releasing hormone (GH-RH) a neuropeptide elaborated by the median eminence of the hypothalamus that binds to specific receptors on the somatotroph cells of the anterior pituitary and stimulates the secretion of
growth hormone.
lactation hormone (
lactogenic hormone)
prolactin.
local hormone a substance with hormone like properties that acts at an anatomically restricted site; most are rapidly degraded. Called also
autacoid and
autocoid.
luteinizing hormone (LH) a
gonadotropin of the anterior pituitary gland, acting with
follicle-stimulating hormone to cause ovulation of mature follicles and secretion of estrogen by thecal and granulosa cells of the ovary; it is also concerned with corpus luteum formation. In the male, it stimulates development of the interstitial cells of the testes and their secretion of testosterone. Called also
interstitial cell–stimulating hormone.
melanocyte-stimulating hormone (MSH) a substance from the anterior
pituitary gland of certain other animals but not humans; it influences the formation or deposition of
melanin in the body and pigmentation of the skin.
parathyroid hormone (PTH) a polypeptide hormone secreted by the
parathyroid glands that influences calcium and phosphorus metabolism and bone formation.
placental h's hormones secreted by the placenta, including
chorionic gonadotropin, and other substances having estrogenic, progestational, or adrenocorticoid activity.
progestational hormone 2. progestational agent.
prolactin-inhibiting hormone a hormone released by the
hypothalamus that inhibits the secretion of
prolactin by the anterior
pituitary gland.
thyrotropin-releasing hormone (TRH) a tripeptide hormone of the hypothalamus, which stimulates release of
thyrotropin from the pituitary gland. In humans, it also acts as a
prolactinreleasing factor. It is used in the diagnosis of mild
hyperthyroidism and Graves disease, and in differentiating between primary, secondary, and tertiary
hypothyroidism.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
hor·mone
(hōr'mōn), A chemical substance, formed in one organ or part of the body and carried in the blood to another organ or part where they exert functional effects; depending on the specificity of their effects, hormones can alter the functional activity, and sometimes the structure, of just one organ or tissue or various numbers of them. Various hormones are formed by ductless glands, but molecules such as secretin, cholecystokinin/somatostatin, formed in the gastrointestinal tract, by definition are also hormones. The definition of hormone has been recently extended to chemical substances formed by cells and acting on neighboring cells (that is, paracrine function) or the same cells that produce them (that is, autocrine function). For hormones not listed below, see specific names.
[G. hormōn, pres. part. of hormaō, to rouse or set in motion]
Farlex Partner Medical Dictionary © Farlex 2012
Patient discussion about Hormone
Q. does the growth hormone have side effects and what are they?
A. Yes, it does, and not a few. They include, among others, pain in the joints, carpal tunnel syndrome, diabetes, pain at the injection site, problems with the thyroid gland, ear problems and many others. You may read more about side effects of growth hormone treatment (called Mecasermin or Somatropin) here: http://www.drugs.com/ppa/mecasermin.html
Q. what is the effect of hormones during pregnancy on a woman's temper?
A. Hormonal changes during pregnancy can indeedn cause mood changes, starting from anxiety or agitations to developing major clinical symptoms of depression. Pregnancy affects each woman differently.
Q. What types of hormonal changes caused by fibromyalgia? Fibromyalgia affects hormones because I feel pain in my back bone. What types of hormonal changes caused by fibromyalgia?
A. Have you ever checked your back pain with a doctor? It may or may not be due to fibromyalgia. Low serotonin levels, low growth hormone levels, and low levels of neuropeptide Y, a component of the feel-good hormone neurotransmitter norepinephrine have been associated with fibromyalgia. Elevated levels of substance P acts as a neurotransmitter and signals the body to experience pain. These pains have also been observed in the spinal cord of fibromyalgia patients.
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