Hormones

Hormones are organic substances that are secreted by plants
and animals and that function in the regulation of physiological
activities and in maintaining homeostasis. They carry out their
functions by evoking responses from specific organs or tissues
that are adapted to react to minute quantities of them. The
classical view of hormones is that they are transmitted to their
targets in the bloodstream after discharge from the glands that
secrete them. This mode of discharge (directly into the
bloodstream) is called endocrine secretion. The meaning of the
term hormone has been extended beyond the original definition
of a blood-borne secretion; however, to include similar regulatory
substances that are distributed by diffusion acro...