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Endocrine Glands

By

John E. Morley

, MB, BCh, Saint Louis University School of Medicine

Last full review/revision Apr 2019| Content last modified Jan 2020
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The endocrine system consists of a group of glands and organs that regulate and control various body functions by producing and secreting hormones. Hormones are chemical substances that affect the activity of another part of the body. In essence, hormones serve as messengers, controlling and coordinating activities throughout the body.

  • Endocrine glands release their hormones directly into the bloodstream

  • Exocrine glands release hormones or other substances into a duct

The individual organs that make up the endocrine system have different and often unrelated functions. Doctors who specialize in disorders of the endocrine system are known as endocrinologists. Many endocrinologists further subspecialize in the functions and disorders of specific glands.

The major glands of the endocrine system, each of which produces one or more specific hormones, are the

Major Endocrine Glands

The major glands of the endocrine system are the hypothalamus, the pituitary gland, the thyroid gland, the parathyroid glands, the islet cells of the pancreas, the adrenal glands, the testes in men, and the ovaries in women.

Major Endocrine Glands

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 digestive tract 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 (how the body uses foods to control chemical processes in the body) and appetite.

Additionally, the term "gland" does not necessarily mean that the organ is part of the endocrine system. For example, sweat glands, salivary glands, glands in mucus membranes, and mammary glands are called exocrine glands, because they secrete substances other than hormones and because they secrete the substances into ducts, not directly into the bloodstream.

The pancreas Pancreas The pancreas is an organ that contains two types of glandular tissue: Pancreatic acini Islets of Langerhans (See also Overview of the Digestive System.) The acini produce digestive enzymes.... read more Pancreas is both an endocrine and exocrine gland. Specialized areas within the pancreas make insulin and other hormones that are released into the bloodstream to regulate the level of sugar in the blood, and other areas make digestive fluids that pass through the pancreatic duct and eventually into the small intestine to help digest food.

Did You Know...

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Test your knowledge
Polyglandular Deficiency Syndromes
Polyglandular deficiency syndromes are hereditary disorders in which several endocrine glands (ie, glands that secrete hormones) malfunction together. Which of the following is the most appropriate treatment for these types of disorders? 
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