Etymology: Gk, para + thyreos, shield, eidos, form; L, glans, acorn
any one of several small structures, usually four, attached to the dorsal surfaces of the lateral lobes of the thyroid gland. The parathyroid glands secrete parathyroid hormone, which helps maintain the blood calcium concentration and ensures normal neuromuscular irritability, blood clotting, and cell membrane permeability. Each parathyroid gland is an oval brownish red disk measuring about 6 by 4 mm. The parathyroids are divided, according to their location, into the superior parathyroids and the inferior parathyroids. The superior parathyroids, usually two, are commonly situated, one on each side, on the caudal border of the cricoid cartilage beside the junction of the pharynx and the esophagus. The inferior parathyroids, also usually two, may be situated on the caudal edge of the lateral lobes of the thyroid gland or adjacent to one of the inferior thyroid veins. These glands are composed of intercommunicating columns of cells bound by connective tissue with a rich supply of capillaries. Parathyroid hypofunction usually causes tetany, which can be treated by the administration of calcium salts or parathyroid extracts.
1. situated beside the thyroid gland.
2. one of the parathyroid glands.
3. a preparation containing parathyroid hormone from animal parathyroid glands; used for diagnosis and treatment of hypoparathyroidism.
parathyroid calcium-regulating hormone
see parathyroid hormone (below).
remnants of the embryonic duct that connects the parathyroid and the thymus during embryogenesis. Called also Kursteiner's cyst.
small body in the region of the thyroid gland, occurring in a variable number of pairs, commonly two.
The parathyroid contains two types of cell: chief cells and oxyphils. Chief cells are the major source of parathyroid hormone (PTH), the secretion of which is dependent on the serum calcium level. Through a closed-loop feedback mechanism a low serum calcium level stimulates secretion of PTH; conversely, a high serum calcium level inhibits its secretion. The essential role of PTH is maintenance of a normal serum calcium level in association with vitamin D and calcitonin.
parathyroid gland hyperplasia
may be focal and nodular or, more importantly diffuse. The latter occurs in cases suffering long-standing nutritional deficiency of calcium or renal insufficiency.
parathyroid hormone (PTH)
a simple, straight-chain polypeptide, synthesized in chief cells and stored in secretory granules. The hormone stimulates the formation and activity of resorptive osteocytes so that calcium is released into body fluids without extensive bone remodeling. This is its mineral homeostatic function and is a relatively quick, short duration response. It is also concerned in skeletal homeostasis by stimulating osteoclastic osteolysis, the slower acting process of bone remodeling.
parathyroid hormone-related protein, parathyroid hormone-like peptide parathyroid hyperfunction parathyroid secretory protein
stored in secretory granules with parathyroid hormone but has no known function. Called also chromogranin A.
carcinomas occur rarely and adenomas more commonly, particularly in older dogs. Either type of tumor may be nonfunctional or functional, causing a primary hyperparathyroidism.