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Definition of HORMONE
: a product of living cells that circulates in body fluids (as blood) or sap and produces a specific often stimulatory effect on the activity of cells usually remote from its point of origin; also: a synthetic substance that acts like a hormone
a: a product of living cells that circulates in body fluids (as blood) or sap and produces a specific often stimulatory effect on the activity of cells usually remote from its point of origin—called also internal secretion; see plant hormoneb: a synthetic substance that acts like a hormone
Organic compound (often a steroid or peptide) that is produced in one part of a multicellular organism and travels to another part to exert its action. Hormones regulate physiological activities including growth, reproduction, and homeostasis in vertebrates; molting and maintenance of the larval state (seelarva) in insects; and growth, bud dormancy, and leaf shedding in plants. Most vertebrate hormones originate in specialized tissues (seeendocrine system; gland) and are carried to their targets through the circulation. Among the many mammalian hormones are ACTH, sex hormones, thyroxine, insulin, and epinephrine. Insect hormones include ecdysone, thoracotropic hormone, and juvenile hormone. Plant hormones include ethylene, abscisin, auxins, gibberellins, and cytokinins.