Physiology: Animal Function and Reproduction

Endocrine System

Who discovered the first known animal hormone?

The British physiologists William Bayliss (1860–1924) and Ernest Starling (1866–1927) discovered secretin in 1902. They used the term “hormone” (from the Greek word horman, meaning “to set in motion”) to describe this chemical substance—one that stimulated an animal’s organ at a distance from the chemical’s site of origin. Their famous experiment using anesthetized dogs demonstrated that diluted hydrochloric acid, mixed with partially digested food, activated a chemical substance in the duodenum. The activated substance secretin was released into the bloodstream and came into contact with cells of the pancreas; in turn, in the pancreas, it stimulated secretion of digestive juice into the intestine through the pancreatic duct.


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