Endocrinology is the study of glands and the hormones they produce. 

Most current concepts have evolved during the last century. In 1849, Berthold demonstrated that castration of a cockerel caused regression of secondary sexual characteristics and mating behaviour. 
He is consequently credited with performing the first recorded experiment in endocrinology.

By 1900, the clinical manifestations of several endocrine diseases had been described, together with their presumed association with glandular dysfunction. 

Among them were descriptions of acromegaly, hypothyroidism, Addisons disease and the recognition of an association between episodic hypertension and adrenal tumours. 
Over the subsequent two decades, adrenaline, thyroxine and the adrenal steroids were successfully isolated. Identification of insulin in 1922 by Banting and Best was a milestone, not only because it enabled treatment for diabetes, but also because it was the first isolation of a peptide hormone. 
Over the next 50 years, many other peptide hormones were isolated, sequenced and their functions described. Important principles of endocrinology, including feedback regulation by hormones produced in target glands, and the concept of hypothalamic-pituitary control of multiple glands, were established. 
The conceptual framework for mechanisms of hormone action was outlined, and in 1963 Berson and Yalow developed the radio-immunoassay as a sensitive and accurate method for measuring plasma hormone levels.

The word hormone is derived from the Greek and means to set in motion. 

All hormones induce dynamic responses at sub-cellular level as well as at the level of whole animal physiology. 

Endocrinology is ultimately the study of communication between cells and different organs. 
Means of communication include peptide hormones or growth factors, amino acid derivatives such as neurotransmitters or thyroxine, or derivatives of cholesterol such as steroids.

Researches are focused in the following areas: neuroendocrine control of feeding and energy expenditure; pathogenesis of insulin expenditure; and molecular mechanisms of thyroid action.