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Without regular supplies of some hormones ourcapacity to behave would be seriously impaired;without others we would soon die. Tiny amounts ofsome hormones can modify moods and actions, ourinclination to eat or drink, our aggressiveness orsubmissiveness, and our reproductive and parentalbehavior. And hormones do more than influenceadult behavior; early in life they help to determine the development of bodily form and may even determine an individuals behavioral capacities.Later in life the changing outputs of some endocrine glands and the bodys changing sensitivity to some hormones are essential aspects of the phenomena of aging. Communication within the body and the consequent integration of behavior wereconsidered the exclusive province of the nervous system up to the beginning of the presentcentury. The emergence of endocrinology as a separate discipline can probably be traced tothe experiments of Bayliss and Starling on the hormone secretion. This substance is secretedfrom cells in the intestinal walls when food enters the stomach; it travels through thebloodstream and stimulates the pancreas to liberate pancreatic juice, which aids in digestion.By showing that special cells secret chemical agents that are conveyed by the bloodstream and regulate distant target organs or tissues. Bayliss and starling demonstrated that chemical integration could occur without participation of the nervous system. The term hormone was first used with reference to secretion. Starling derived the termfrom the Greek hormone, meaning to excite or set in motion. The term endocrine wasintroduced shortly thereafter Endocrine is used to refer to glands that secret products intothe bloodstream. The term endocrine contrasts with exocrine, which is applied to glands thatsecret their products though ducts to the site of action. Examples of exocrine glands are thetear glands, the sweat glands, and the pancreas, which secrets pancreatic juice through aduct into the intestine. Exocrine glands are also called duct glands, while endocrine glands arecalled ductless. | 
