Group of ductless gland s that secrete hormone s necessary for normal growth and development, reproduction, and homeostasis .
The major endocrine glands are the hypothalamus , thyroid , islets of Langerhans , adrenal s, parathyroid s, 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. {{link=tumour">Tumour s that produce hormones can throw off this balance. Diseases of the endocrine system result from over-or underproduction of a hormone or an abnormal response to a hormone.