Endocrinology

Endocrinology is a branch of medicine dealing with disorders of

Background

As evolution drove the emergence of multicellular organisms it became necessary to develop ?coordinating systems to regulate and integrate the function of differentiating cells? (Griffin and Ojeda 2000). Two mechanisms perform this function in higher animals, the nervous system and the endocrine system. Unlike the former, which sends and receives information via electrochemical signals, the endocrine system performs its regulatory function through the detection, production and release (generally into the bloodstream) of chemical agents. The proper function of this system is vital to the proper development of organisms. As Hadley (2000) notes, the integration of developmental events such as proliferation, growth, differentiation (including histogenesis and organogenesis) and the coordination of metabolism, respiration, excretion, movement, reproduction and sensory perception are dependant on ?chemical cues, substances synthesised and secreted by the specialised cells within the animal?.

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Endocrinology concerns itself with the study of the endocrine system, primarily the biosynthesis, storage, chemistry and physiological function of the ?chemical cues? or hormones (a term coined in 1902 ? from the Greek όρμάω ?I excite? or ?I arouse? (Chester-Jones et al 1987)) but also the cells of the endocrine glands and tissues that secrete them. It is also important to consider the mechanism of, and factors controlling, hormone secretion; the mechanisms of hormone action and receptor binding; the pathophysiology of endocrine system dysfunction and the effect of exogenous substances on normal function.

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The study of endocrinology effectively began with a study by Berthold (1849), largely ignored at the time, in which he noted that castrated cockerels failed to develop combs and wattles or exhibit overtly male behaviour. It was further noted that the replacement of testes back into the abdominal cavity of either the same bird or another castrated individual resulted in normal behavioural and morphological development. Berthold concluded, rather erroneously, that the testes secreted a substance that conditioned the blood (since they could no longer be nervously enervated) that, in turn, acted upon the body of the cockerel. In fact, one of two other things could have been true based on these data: that the testes modified or activated a constituent of the blood or that the testes removed an inhibitory factor from the blood. It was not proven that the testes released a substance that engenders male characteristics until it was shown that the extract of testes could replace their function in castrated animals. Pure, crystalline testosterone was isolated in 1935 by David et al.

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Although most of the relevant tissues and endocrine glands had been extensively identified and categorised by early anatomists (and, later, microscopists) a more humoural approach to understanding biological function and disease was favoured by classical thinkers such as Aristotle, Hippocrates, Lucretius, Celsus and Galen according to Freeman et al (2001) and these theories held sway until the advent of germ theory, physiology and organ basis of pathology in the 19th Century.

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