Group of ductless glands that secrete hormones necessary for normal growth and development, reproduction, and homeostasis. In humans, the major endocrine glands are the hypothalamus, pituitary, pineal, thyroid, parathyroids, adrenals, islets of Langerhans in the pancreas, ovaries, and testes. Secretion is regulated either by regulators in a gland that detect high or low levels of a chemical and inhibit or stimulate secretion or by a complex mechanism involving the hypothalamus and the pituitary. Tumours that produce hormones can throw off this balance. Diseases of the endocrine system result from over- or underproduction of a hormone or from an abnormal response to a hormone.
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