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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.
adrenocorticotropic hormone (ACTH) corticotropin.
adrenomedullary h's substances secreted by the adrenal medulla, including epinephrine and norepinephrine.
androgenic hormone androgen.
anterior pituitary hormone any of the protein or polypeptide hormones secreted by the anterior lobe of the pituitary gland, including growth hormone, thyrotropin, prolactin, follicle-stimulating hormone, luteinizing hormone, melanocyte-stimulating hormone, and corticotropin.
antidiuretic hormone (ADH) vasopressin.
corpus luteum hormone progesterone.
cortical hormone corticosteroid.
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.
estrogenic hormone estrogen.
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.
follicle-stimulating hormone and luteinizing hormone–releasing hormone (FSH/LH-RH) luteinizing hormone–releasing hormone.
follicle-stimulating hormone–releasing hormone (FSH-RH) luteinizing hormone–releasing hormone.
gonadotropic hormone gonadotropin.
gonadotropin-releasing hormone (Gn-RH) luteinizing hormone–releasing hormone.
growth hormone (GH) any of several related polypeptide hormones secreted by the anterior lobe of the pituitary gland that directly influence protein, carbohydrate, and lipid metabolism and control the rate of skeletal and visceral growth; their secretion is in part controlled by the hypothalamus. It is used pharmaceutically as somatrem and somatropin. Called also somatotrophin, somatotropin, and somatotrophic or somatotropic hormone.
growth hormone release–inhibiting hormone somatostatin.
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.
interstitial cell–stimulating hormone luteinizing 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.
luteinizing hormone–releasing hormone (LH-RH) a decapeptide hormone of the hypothalamus, which stimulates the release of follicle-stimulating hormone and luteinizing hormone from the pituitary gland; it can be used in the differential diagnosis of hypothalamic, pituitary, and gonadal dysfunction. Called also follicle-stimulating hormone–releasing hormone, follicle-stimulating hormone and luteinizing hormone–releasing hormone, and gonadotropin-releasing 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.
neurohypophyseal h's those stored and released by the neurohypophysis, i.e., oxytocin and vasopressin.
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.
prolactin-releasing hormone any of various hormones elaborated by the hypothalamus that stimulate the release of prolactin by the anterior pituitary gland. Most such activity is exerted by vasoactive intestinal polypeptide, although in humans thyrotropin-releasing hormone can also have this action.
sex h's see sex hormones.
somatotrophic hormone (somatotropic hormone) growth hormone.
somatotropin release–inhibiting hormone somatostatin.
somatotropin-releasing hormone (SRH) growth hormone–releasing hormone.
steroid h's hormones that are biologically active steroids; they are secreted by the adrenal cortex, testis, ovary, and placenta and include the progestational agents, glucocorticoids, mineralocorticoids, androgens, and estrogens. They act by binding to specific receptors to form complexes, which then enhance or inhibit the expression of specific genes.
thyroid h's see thyroid hormones.
thyroid-stimulating hormone (TSH) thyrotropin.
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.


follicle-stimulating hormone–releasing hormone.
See: hormone