The Endocrine Glands
T echnically speaking, a gland is any cell or organ in our bodies that secretes some substance. In this broad sense, our liver is a gland, because one of its many functions is to secrete bile. So too, is the placenta that encloses a developing baby and supplies it with chemicals that assure normal growth. Even the brain has been shown by modern research to secrete special substances. But lymph glands are not considered true glands and are more correctly called lymph nodes.
Physicians divide the glands into two categories. Endocrine glands are also known as ductless glands , because they release their secretions directly into the bloodstream. Exocrine glands , by contrast, usually release their substances through a duct or tube. Exocrine glands include the sebaceous and sweat glands of the skin; the mammary or milk glands; the mucous glands, some of which moisten the digestive and respiratory tract; and the salivary glands, whose secretions soften food after it enters the mouth. The pancreas has both an endocrine and an exocrine function and structure.