Endocrine Glands

Abstract

Endocrine glands are ductless, and their products are secreted into the interstitial space of their surrounding connective tissue and then pass into blood vessels. Hence the term endocrine, which means secreting internally. Such glands constitute one oftwo major mechanisms for initiation, integration, and correlation of adjustments to internal and external environmental variations. The other is the nervous system, in which neurons transmit signals as a result of environmental alteration, in the form of waves of depolarization that initiate a distant response. An endocrine gland, in response to a specific stimulus (which may be neural or hormonal), releases into the circulation a chemical messenger that brings about appropriate specific responses in other tissues or organs. The substance is termed a hormone, from the Greek meaning “to set in motion.”