Medical discipline dealing with regulation of body functions by hormones and other biochemicals and treatment of endocrine system imbalances. In 1841 Friedrich Gustav Henle first recognized ductless glands, which secrete products directly into the bloodstream. The field was essentially established in the early 20th century, when Ernest H. Starling, who introduced the term hormone, proposed that chemical and nervous regulation of physiological processes were linked. Endocrine therapy is based on replacing deficient hormones with purified extracts. Nuclear technology has led to new treatments; use of radioactive iodine for hyperthyroidism greatly reduced the need for thyroid gland surgery. The detection of minute amounts of hormone with radioimmunoassays (seeradiology) permits early diagnosis and treatment of endocrine disorders.