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1. A chemical released by a cell, a gland, or an organ in one part of the body that affects cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one cell to another. (

2. (Endocrinology) A naturally occurring substance secreted by specialized cells that affects the metabolism or behavior of other cells possessing functional receptors for the hormone. Hormones may be hydrophilic, like insulin, in which case the receptors are on the cell surface or lipophilic, like the steroids, where the receptor can be intracellular. (

3. A regulatory substance produced in an organism and transported in tissue fluids such as blood or sap to stimulate specific cells or tissues into action. (Google Dictionary)

4. (Physiology) Any substance produced by one tissue and conveyed by the bloodstream to another to effect physiological activity. (

5. (Pharmacology) A synthetic compound with the same activity. (

6. Any similar substance in plants. (

Word origin: From Greek hormon “that which sets in motion,” present participle of horman “impel, urge on,” from horme “onset, impulse,” from PIE *or-sma-, from root *er- “to move, set in motion.”

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