Clinical endocrinology is a branch of Medicine that deals with the endocrine glands, actions of hormones and their metabolic consequences.
Since hormones act on virtually every organ and cell type in the body, the endocrinologist needs to have a definitive knowledge about medicine.
Some disorders lie very clearly and totally within the domain of the endocrinologists, being entirely or largely due to an abnormality of hormone production. This includes diabetes that is caused due to decreases secretion of insulin from pancreas (Type 1 diabetes) or hypothyroidism that is caused due to decreased secretion of thyroid hormone from the thyroid glands.
Yet other diseases are not exactly of endocrine origin but have aspects of endocrinology in them. This includes examples such as osteoporosis or infertility. In these cases the endocrinologist may need to work with a physician or a gynaecologist and a multidisciplinary approach is appropriate.
History of endocrinology
History of endocrinology and study of hormone function dates back to 400 BC when Hippocrates brought forth the Humoral Hypothesis. Aristotle noted there were changes in physical and behavioral aspects after castration on roosters.
It was noted that pre-pubertal castration in humans led to short stature, long arms, no facial hair or pubertal change in voice. These eunuchs guarded the doors of the queens and noble women in ancient times.
17th and 18th century common practices
Once a common practice in Europe and Asia involved castrating young boys with singing voices to prevent the pubertal changes in voice and use them as choir boys. Popularity reached a peak in 17th and 18 centuries. These boys were called Castrati and had a range of a soprano, but greater development of the male lungs meaning more power.
The first recorded hormone experiments
The first recorded endocrine experiment and noted researchers who were experimenting with hormones and circulation were William Harvey (1628), John Hunter (late 1600’s) and Bordeau (1775). Arnold Berthold conducted the first experiment showing constancy of the Internal Environment.
Claude Bernard (in 1872) found that a regulated internal environment (le milieu intérieur) in a changing, and challenging, environment was noteworthy. He noted that cells and tissues need to communicate for coordination of physiological activities.
Charles Brown-Séquard, a French physician, first studied Endocrine Replacement Therapy or replacement of deficient hormones within the body by supplementing it from outside. Von Mering and Menkoski removed the pancreas from dogs and noticed changes in urine and blood glucose.
The first described hormone
The first described hormone (1902) was a result of efforts by Sir William Bayliss (1860-1924) and Ernest Starling (1866-1927). In response to the delivery to the intestine of acidic chyme from the stomach, endocrine cells of the duodenun release secretin (an internal secretion) into the bloodstream.
The researchers found that Secretin stimulates the exocrine pancreas to secrete bicarbonate into the intestine to neutralize the acid. In 1902 epinephrine was purified and it was synthesized in 1904.
Between 1900 and 1930’s was a period of research on biochemistry, reproductive cycles, and surgery. In 1920-1930 Adrenalectomy (removal of adrenal glands) and hypophosectomy (removal of pituitary glands) were perfected and all steroid hormones were discovered.
In 1940-1950 radioisotopes, culturing methods, electron microscope were used in experiments. Between 1950’s and 1960’s detailed biochemistry and mechanisms of action were studied.
- Frederick Sanger determined the structure of insulin (1958) and this was a landmark achievement in endocrinology. Hormone Structure, Synthesis and Assay was perfected.
- Vincent du Vigneaud synthesized polypeptide hormones (oxytocin and vasopressin) in 1955.
- Rosalyn Yalow developed radioimmunoassay for measurement of hormone concentrations in 1977.
- Katsoyannis synthesized insulin in 1963.
At present endocrinology deals with major aspects like:
- Scientific – Dealing with discovery and assaying the structures and functions of various hormones
- Clinical – This deals with the clinical disorders of endocrine system and their complex pathophysiology and management.
- Food Production – Endocrinology and genetic engineering in conjunction are being widely used in increasing animal produce like meat, eggs, milk etc.