human endocrine system, 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.
human endocrine system summary
parathyroid gland summary
parathyroid gland, Endocrine gland located close to and behind the thyroid gland. Humans typically have four parathyroid glands. Each gland secretes parathyroid hormone, which regulates blood calcium and phosphate levels. When serum calcium concentrations drop, increased hormone secretion releases calcium from bone into the bloodstream (see calcium deficiency). An increase in parathyroid hormone secretion also increases excretion of phosphate in the urine, thereby lowering serum phosphate concentrations. In addition, the hormone regulates magnesium metabolism by increasing its excretion. When thyroid removal is required, the parathyroid glands must be separated out and left in place to avoid hypoparathyroidism (parathyroid hormone deficiency). See also endocrine system.