Discovery of Hormones

British physiologists William Bayliss and Ernest Starling discovered the first known hormone in 1902 while investigating how the pancreas is triggered to release digestive secretions, finding that pancreatic secretion continued even after every nerve connecting the pancreas to the rest of the body had been severed, which showed that a chemical signal, rather than a nerve impulse, was responsible. They identified the substance responsible, a compound released by the intestine into the bloodstream that stimulated the pancreas from a distance, and named it secretin; in 1905, Starling coined the general term hormone, from a Greek word meaning to arouse or excite, defining hormones as chemical messengers that travel through the bloodstream to coordinate the activity and growth of different parts of the body. Although the adrenal hormone adrenaline had already been isolated by George Oliver and Edward Schafer in 1894, it was Bayliss and Starling's identification of secretin, and Starling's naming of the broader class of substance it belonged to, that established hormonal signaling as a distinct and general principle of the body's coordination systems, founding the science of endocrinology.