THE ENDOCRINE GLANDS - Preventive care

THE ENDOCRINE GLANDS 

UNTIL ABOUT a century ago, the nervous system was generally credited with being the one controlling force for complex body processes. But then it became evident that some other influence must be at work. Too many phenomena appeared to have no relationship to the nervous sys- tem. It was difficult to explain-in terms of the nervous system alone- the differences in size among people, body changes of puberty, variations of vigor and energy.

 The explanation was to be found in certain glands, the endocrines, which are not at all like the salivary, sweat, and other exocrine glands. The exocrine are glands of external secretion. They pour their products through ducts or tubes, and the secretions have purely local activity. In- deed, the ducts carry them to the sites where they serve self-evident purposes. 

The endocrines are glands of internal secretion. They have no ducts. Instead, their secretions go into the bloodstream, and their effects are felt in areas far removed from the sites of the glands. The existence of some of these glands was long known.

 It was long clear, for example, that there was a connection between the sex glands -testes and ovaries-and secondary sexual characteristics such as male beards and female breast development. It had been apparent enough for centuries that when a boy's testes were destroyed, he failed to develop masculine characteristics. Now much more is known about the sex and other endocrine glands and the activities of the substances they secrete, called hormones, as powerful chemical regulators. 

Hormones control the size, shape, and appearance of the body; influence emotions and mental state; team up with the nervous system in determining, essentially, the kind of individual you me and oven to some extent how you live. The exact chemical composition of many of these hormones has been established. They have been extracted in pure form from the glands-in many instances, from equivalent animal glands-for medical use. 

Some have been created synthetically in the laboratory. Much has been learned about the exact functions of the various hormones and the consequences when a specific gland fails to function properly, creating too much or too little of its hormone or hormones. Endocrinology is still a young science with much to learn, but some of the most remarkable advances in medicine have come as the result of advances in endocrinology.