parathyroid

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parathyroid

 [par″ah-thi´roid]
1. near the thyroid 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.

par·a·thy·roid

(par'ă-thī'royd),
1. Adjacent to the thyroid gland.
2. Synonym(s): parathyroid gland

parathyroid

(păr′ə-thī′roid)
adj.
1. Of, relating to, or obtained from the parathyroid glands: a parathyroid extract.
2. Adjacent to the thyroid gland.
n.
1. Any of the parathyroid glands.
2. A parathyroid hormone.

parathyroid

adjective Referring to the parathyroid gland.

noun Parathyroid gland (see there); glandulae parathyroideae [NA6].

par·a·thy·roid

(par'ă-thī'royd)
1. Adjacent to the thyroid gland.
2. Synonym(s): parathyroid gland.

parathyroid

an endocrine gland of higher vertebrates that is situated in or near the thyroid gland and controls the calcium level of the blood. When too little [Ca+] is present in the blood, parathormone is secreted which:
  1. (a) reduces the OSTEOBLAST activity and thus the amount of bone-matrix formation,
  2. (b) increases [Ca+] uptake from the gut into the blood stream, and
  3. (c) acts on the kidney tubules, decreasing calcium and phosphate excretion. Undersecretion of parathormone results in a fall of blood calcium and causes TETANY.