A chemical signal in the body of an organism. Most hormones transmit signals between cells, but some (pheromones) transmit signals between different organisms, while other hormone-like signal molecules transmit signals within a cell. Synthetic substances can function as hormones either as medicines or unintended environmental pollutants. Hormones can be proteins, steroids, and depending on how you look at it, even nucleotides and ions.

hormone: a chemical messenger secreted into the bloodstream from specialized glandular cells, including those of the endocrine glands, of the brain and neuroendocrine systems, and of some visceral tissues. It carries information to other cells and organs of the body. A body chemical secreted from specialized glandular cells, especially in the endocrine glands, and carried in the bloodstream for use in other parts and cells of the body. See also pheromone.

Dictionary of Sexology Project: Main Index

Hormones are protein or steroid substances secreted by the ductless (endocrine) glands to serve as blood-borne "messengers" that regulate cell function elsewhere in the body. They form a communications system in the body and can bring about extraordinary changes in cell activity.

Hormones exert their effects by altering the rates at which specific cellular processes proceed. For example, insulin promotes glucose (sugar) uptake by cells that require energy; follicle-stimulating hormone provokes the ovary into producing ovum; testosterone enhances the production of spermatozoa in the testes. The hormones do this by combining with enzymes, or by enhancing enzyme production in a cell through a chemical effect on the RNA (ribonucleic acid) of the cell. The result in the body depends on the target organ cell of the hormone and its function.

The nervous and endocrine systems of the body actually function as a single interrelated system. The central nervous system, particularly the hypothalamus, plays a crucial role in controlling hormone secretion; conversely, hormones greatly alter neural function. No hormone is secreted at a constant rate, and most hormones are either broken down by the liver or excreted by the kidneys. The investigation of endocrine disease therefore depends on measurements of excretion rates and circulating blood levels; but since many of these chemical messengers are bound to protein in the blood, the diagnostic tests are particularly complicated and expensive.

Disease in the endocrine system is revealed by an alteration in the expected effects of the target organ cells. For example, growth fails to occur, ovulation is inadequate, or myxedema occurs because of inadequate function of the thyroid gland. Less frequently the disorder may be that of excessive hormonal secretion, for example, virilization in a woman from a pituitary tumor, or thyrotoxicosis from a thyroid tumor. The treatment of hormonal disorder is undertaken by an endocrinologist and involves the achievement of balance in the supplements administered; diabetic control by the appropriate daily dosage of insulin is the clearest example of this.

In therapy, hormones are used as replacement where the patient is deficient (as with insulin for the diabetic), as treatment to overcome disease (for example, cortisone for arthritis or asthma), and as controlling agents to divert natural functions (for example, sex hormones as contraceptives). Synthetic compounds, designed to resemble the natural products but to achieve enhanced or differing effects, have gradually become available since the 1930s, and in recent years an explosive increase in the knowledge of their benefits---and their disadvantages---has been achieved.

Considerable improvements in the effectiveness of hormone treatment and replacement therapy have been made, but the accurate elucidation of each hormone's multiple influences on human physiology is a continuing challenge.

A biochemical substance that is produced by a specific cell or tissue and causes a change or activity in a cell or tissue located elsewhere in an organism.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.

Hor"mone (hôr"môn), n. [From Gr. "orma`ein to excite.] (Physiol. Chem.)

A chemical substance formed in one organ and carried in the circulation to another organ on which it exerts a stimulating effect; thus, according to Starling, the gastric glands are stimulated by a hormone from the pyloric mucous membrane.


© Webster 1913.

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