ABSTRACT
In multicellular organisms, physiological functions are regulated by both the nervous system and the endocrine system. Endocrine glands synthesize and release physiologically active substances – hormones. These hormones are generally released into the vascular system whereupon they are transported to their target tissue where they produce their physiological effects. The target tissue may be a further endocrine gland or it may be a non-endocrine structure. In some instances, e.g. in the case of so-called local hormones, endocrine tissue secretes hormones but this secretion is not into the vascular system. Instead, the released hormone diffuses in interstitial fluid to an adjacent tissue where it produces its physiological effect – hence the term local hormone.
