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  Endocrinology (Greek endo, ‘inside’, krino, ‘sift’ + ology), in the life sciences, is the study of the systems of internal body secretions, which are collectively termed hormones. These chemical messenger substances are secreted into the blood by endocrine glands and circulate throughout the bloodstream; where they come into contact with tissues which are sensitized to them (target organs) they produce an effect. A wide range of functions is under a degree of hormonal control, from menstruation to lactation and from thirst to the formation of urine. Some hormones act on endocrine glands so that the system may be partly self-regulating. Other endocrine systems are regulated by negative feedback, in which hormone secretion is inhibited by some product of the changes which the hormone initiates.

The first hormone, adrenaline, was isolated by the Japanese chemist Jokiche Takamine (1854 - 1922), after it had been observed that extracts of the adrenal gland could raise blood pressure. As the 20th century has progressed many other hormones have been discovered, often during the course of investigations into human disorders. Most important of all was the discovery of insulin in 1921 by the Canadian physician Frederick Banting. Insulin is a hormone that plays a central role in the control of sugar metabolism; lack of insulin results in diabetes mellitus, a disease which was usually fatal before insulin replacement was possible. Today, insulin and many other hormones, such as human growth hormone and steroid hormones, can be synthesized artificially and used in medicine and research. Contraceptive pills are based on the steroid sex hormones progesterone and oestrogen. RB

See also homeostasis; metabolism; phenology; synergism; tropism.Further reading Mac Hadley, Endocrinology.



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