hormone /hôr″mōn/ [Gk, hormaein, to set in motion] , a complex chemical substance produced in one part or organ of the body that initiates or regulates the activity of an organ or a group of cells in another part. Hormones secreted by the endocrine glands are carried through the bloodstream to the target organ. Secretion of these hormones is regulated by other hormones, by neurotransmitters, and by a negative feedback system in which an excess of target organ activity or hormone signals a decreased need for the stimulating hormone. Other hormones are released by organs for local effect, most commonly in the digestive tract.
