parathyroid /par·a·thy·roid/ (-thi´roid)
parathyroid [par″ah-thi´roid]
1. situated beside the thyroid gland.
2. see under gland.
par·a·thy·roid (p r  -th  roid)adj. 1. Adjacent to the thyroid gland. 2. Of, relating to, or obtained from the parathyroid glands. n. 1. Either of the parathyroid glands. 2. A parathyroid hormone. |
parathyroid [par″ah-thi´roid]
1. near the thyroid gland.
2. a parathyroid gland.
3. a preparation containing parathyroid hormone from animal parathyroid glands; used for diagnosis and treatment of hypoparathyroidism.
parathyroid glands four small endocrine bodies in the region of the thyroid gland; they contain two types of cells: 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. It does this by exerting its effects on bone, kidney, and gastrointestinal tract. In bone, it enhances bone resorption by increasing digestion of the bone matrix by osteoclasts, which produces calcium that gets released into the bloodstream. In the kidney, PTH increases the excretion of phosphate and the reabsorption of filtered calcium. In the intestine, it increases intestinal absorption of calcium. The parathyroid glands may be subject to either hyperparathyroidism or hypoparathyroidism.
parathyroid
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).
parathyroid cyst
remnants of the embryonic duct that connects the parathyroid and the thymus during embryogenesis. Called also Kursteiner's cyst.
parathyroid gland
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
associated with humoral hypercalcemia of malignancy (HHM); see pseudohyperparathyroidism.
parathyroid hyperfunction
parathyroid secretory protein
stored in secretory granules with parathyroid hormone but has no known function. Called also chromogranin A.
parathyroid tumors
carcinomas occur rarely and adenomas more commonly, particularly in older dogs. Either type of tumor may be nonfunctional or functional, causing a primary hyperparathyroidism.
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