Endocrine System

Although some ancient cultures noted biological observations grounded in endocrine function, modern understanding of endocrine glands and how they secrete hormones has evolved only in the last 300 years. Ancient Egyptian and Chinese civilizations castrated (removed the testicles of) a servile class of men called eunuchs. It was noted that eunuchs were less aggressive than other men, but the link of this behavior to testosterone was not made until recently.

Light was shed on endocrine function during the seventeenth and eighteenth centuries by a few significant advances. A seventeenth century English scientist, Thomas Wharton (1614-1673), noted the distinction between ductile and ductless glands. In the 1690s, a Dutch scientist named Fredrik Ruysch (1638-1731) first stated that the thyroid secreted important substances into the blood stream. A few decades later, Theophile Bordeu (1722-1776) claimed that "emanations" were given off by some body parts that influenced functions of other body parts.

One of the greatest early experiments performed in endocrinology was published by A. A. Berthold (1803-1861) in 1849. Berthold took six young male chickens, and castrated four of them. The other two were left to develop normally and used comparatively as control samples. Two of the castrated chickens were left to become chicken eunuchs. But what Berthold did with the other two castrated chickens is what really changed endocrinology. He transplanted the testes back into these two chickens at a distant site from where they were originally. The two castrated chickens never matured into roosters with adult combs or feathers. But the chickens who received transplanted testes did mature into normal adult roosters. This experiment revealed that hormones that could access the blood stream from any site would function correctly in the body and that hormones did, in fact, travel freely in the circulation.

The same year Berthold published his findings, Thomas Addison (1793-1860), a British scientist reported one of the first well documented endocrine diseases which was later named Addison's disease (AD). AD patients all had a gray complexion with sickly skin; they also had weak hearts and insufficient blood levels of hemoglobin necessary for oxygen transport throughout the body. On autopsy, each of the patients Addison studied were found to have diseased adrenal glands. This disease can be controlled today if it is detected early. President John F. Kennedy suffered from AD.