Overview

Hormones are chemical messengers secreted mainly by the body's complex network of glands and glandular tissue that comprise the endocrine system. Each hormone has a unique function and travels via the bloodstream to exert influence upon its targeted cells, tissues, or organs. Hormones affect many vital life functions, stimulating certain life processes, while retarding others. Among other functions, hormones regulate reproduction, the body's fluid balance, growth, and metabolism. The nervous system also acts in conjunction with hormones to enable the body to react to sudden internal or external changes in environment.

After almost 50 years of experimentation, the fledgling science of endocrinology (the study of hormones and their effects on the body) exploded in the 1920s with the discovery of the hormone insulin. Insulin, necessary for the regulation of carbohydrate metabolism, offered the first effective treatment for diabetes...