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A hormone
(from the Greek participle “ὁρμῶν”, "setting in motion")
is any member of a class of signaling
molecules produced by
glands in multicellular
organisms that are transported by the circulatory system
to target distant organs
to regulate physiology and behavior.
Hormones have diverse chemical structures, mainly of three classes: eicosanoids, steroids, and amino acid/protein derivatives (amines, peptides, and proteins). The glands that secrete hormones comprise the endocrine signaling system. The term hormone is sometimes extended to include chemicals produced by cells that affect the same cell (autocrine or intracrine signalling) or nearby cells (paracrine signalling).

Hormones are used to communicate between organs and tissues for physiological regulation and behavioral activities, such as