The major glands of the endocrine system, each of which produces one or more specific hormones, are the hypothalamus, the pituitary gland, the thyroid gland, the parathyroid glands, the islets of the pancreas, the adrenal glands, the testes in men, and the ovaries in women. During pregnancy, the placenta also acts as an endocrine gland in addition to its other functions.
Not all organs that secrete hormones or hormonelike substances are considered part of the endocrine system. For example, the kidneys produce the hormone renin to help control blood pressure and the hormone erythropoietin to stimulate the bone marrow to produce red blood cells. In addition, the gastrointestinal system produces a variety of hormones that control digestion, affect insulin secretion from the pancreas, and alter behaviors, such as those associated with hunger. Fat (adipose) tissue also produces hormones that regulate metabolism and appetite. Additionally, the term "gland" does not mean that the organ is part of the endocrine system. For example, sweat glands, glands in mucus membranes, and mammary glands secrete substances other than hormones.
Last full review/revision May 2006 by John E. Morley, MB, BCh