Hormones can be classified by they are secreted directly into the blood stream, whether they are secreted via a duct, how far they travel and what cells they stimulate. For example, exocrine hormones are secreted into a duct and usually travel far to stimulate distant cells.
Cells that release paracrine hormones secrete these hormones into the
and these hormonal chemicals travel to a
embedded in the membranes of other cells.