Definition: A chemical substance, formed in one organ or part of the body and carried in the blood to another organ or part where they exert functional effects; depending on the specificity of their effects, hormones can alter the functional activity, and sometimes the structure, of just one organ or tissue or various numbers of them. Various hormones are formed by ductless glands, but molecules such as secretin, cholecystokinin/somatostatin, formed in the gastrointestinal tract, by definition are also hormones. The definition of hormone has been recently extended to chemical substances formed by cells and acting on neighboring cells (paracrine function) or the same cells that produce them (autocrine function). For hormones not listed below, see specific names.
[G. hormon, pres. part. of hormao, to rouse or set in motion]
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