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 (see larva ) in insects; and growth, bud dormancy, and leaf shedding in plants. Most vertebrate hormones originate in specialized tissues (see endocrine 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, auxin s, gibberellins, and cytokinins.