The human endocrine system is comprised of several glands which secrete hormones (for example, insulin, thyroxine, cortisol, parathyroid hormone, antidiuretic hormone) into the bloodstream.  These compounds then circulate to target tissues whose physiology they alter to produce a response.  

Endocrine diseases are often characterized by a deficiency of a hormone or an excess of a hormone, with characteristic symptoms associated with each state. 

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