parathyroid glands

(pâr'əthī`roid), four small endocrine bodies, located behind the thyroid gland, that govern calcium and phosphorus metabolism. These four masses of tissue (each about the size of a pea) are difficult to distinguish from the thyroid and are often embedded in it. Consequently, before their significance was known they were sometimes accidently removed during thyroid surgery, causing a deficiency in parathormone, the parathyroid hormone. Parathormone increases the concentration of calcium ions in the blood, with accompanying bone absorption and increased reabsorption of calcium ions by the kidneys. The hormone's effect on phosphate ion concentration is the opposite, i.e., phosphate ion concentration in the bloodstream decreases as a result of increased phosphate excretion by the kidneys. Excessive secretion of parathormone, e.g., caused by tumor of the parathyroid glands, is a serious disorder, for excessive blood calcium can cause kidney stones and long-term weakening of the bones. Undersecretion of parathormone, which can be caused by congenital and metabolic disorders, results in too little calcium in the bloodstream, and too much phosphorus. The result is tetany, i.e., violent muscle spasms.

Parathyroid Glands

organs of internal secretion in man and vertebrates, excluding fish. A number of mammals, such as mice, rats, moles, shrews, hedgehogs, swine, and seals, have one pair of parathyroid glands, while bats, dogs, rabbits, cats, guinea pigs, camels, sheep, goats, and man have two pairs, located on the surface of the thyroid gland or embedded in its tissue.

The parathyroids consist of glandular epithelial tissue, including chief and oxyphile cells arranged in clusters and bands between the capillaries, covered with a connective-tissue capsule. The chief cells are polygonal in shape; their cytoplasm contains a large number of mitochondria, is weakly basophilic, and stains with difficulty. The cytoplasm of oxyphile cells is readily stained by acid dyes. Both types of cells contain special corpuscles consisting of endoplasmic reticular plates, which are probably the centers of synthesis in the cells.

The parathyroid glands produce parathyroid hormone (parathormone), which helps regulate calcium and phosphorus metabolism. There are reciprocal relations between the calcium and phosphorus concentrations in the blood. Calcium and phosphorus homeostasis is maintained by the influence of parathyroid hormone on bone tissue and on the kidneys. An excess of the hormone causes demineralization of the bone tissue and the excretion of calcium and phosphorus from the body. Excess phosphorus is excreted by the kidneys. Softening of bones and their eventual spontaneous fracture occur in hyperparathyroidism; tooth development is slowed in hypoparathyroidism. The administration of parathyroid hormone relieves the symptoms of parathyroid deficiency. Removal of the glands results in convulsions (tetany), caused by the sharp decrease in the blood’s calcium concentration (from 9–11 to 4.5–5 mg percent). Blood phosphorus increases at the same time. Attacks of tetany may occur in animals with normal parathyroids when their food contains insufficient calcium. The size and functional condition of the parathyroids vary with the blood calcium level.

REFERENCES

Leites, S. M., and N. N. Lapteva. Ocherki po patofiziologii obmena veshchestv i endokrinnoi sistemy. Moscow, 1967.
Eskin, I. A. Osnovy fiziologii endokrinnykh zhelez. Moscow, 1968.
Clegg, P., and A. Clegg. Gormony, kletki, organizm. Moscow, 1971. (Translated from English.)

V. M. SAMSONOVA

parathyroid glands

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 glands

Four, yellow, bean-shaped bodies, each about 0.5 cm long, lying behind the THYROID GLAND, usually embedded in its capsule. The parathyroids secrete a hormone, parathyroid hormone (parathormone or PTH), into the blood if the level of calcium in the blood drops. This hormone promotes the release of calcium from the bones, controls loss in the urine and increases absorption from the intestine, thus correcting the deficiency in the blood. Maintenance of accurate levels of blood calcium is more important, physiologically, than the strength of the bones. Secretion of abnormal quantities of PTH from a parathyroid tumour can lead to bone softening. Underaction of the parathyroids causes a dangerous drop in the blood calcium.

Sandström,

Ivor V., swedish anatomist, 1852-1889. Sandström bodies - Synonym(s): parathyroid glands

单词	parathyroid glands
释义	DictionarySeeparathyroid gland parathyroid glands parathyroid glands (pâr'əthī`roid), four small endocrine bodies, located behind the thyroid gland, that govern calcium and phosphorus metabolism. These four masses of tissue (each about the size of a pea) are difficult to distinguish from the thyroid and are often embedded in it. Consequently, before their significance was known they were sometimes accidently removed during thyroid surgery, causing a deficiency in parathormone, the parathyroid hormone. Parathormone increases the concentration of calcium ions in the blood, with accompanying bone absorption and increased reabsorption of calcium ions by the kidneys. The hormone's effect on phosphate ion concentration is the opposite, i.e., phosphate ion concentration in the bloodstream decreases as a result of increased phosphate excretion by the kidneys. Excessive secretion of parathormone, e.g., caused by tumor of the parathyroid glands, is a serious disorder, for excessive blood calcium can cause kidney stones and long-term weakening of the bones. Undersecretion of parathormone, which can be caused by congenital and metabolic disorders, results in too little calcium in the bloodstream, and too much phosphorus. The result is tetany, i.e., violent muscle spasms. Parathyroid Glands organs of internal secretion in man and vertebrates, excluding fish. A number of mammals, such as mice, rats, moles, shrews, hedgehogs, swine, and seals, have one pair of parathyroid glands, while bats, dogs, rabbits, cats, guinea pigs, camels, sheep, goats, and man have two pairs, located on the surface of the thyroid gland or embedded in its tissue. The parathyroids consist of glandular epithelial tissue, including chief and oxyphile cells arranged in clusters and bands between the capillaries, covered with a connective-tissue capsule. The chief cells are polygonal in shape; their cytoplasm contains a large number of mitochondria, is weakly basophilic, and stains with difficulty. The cytoplasm of oxyphile cells is readily stained by acid dyes. Both types of cells contain special corpuscles consisting of endoplasmic reticular plates, which are probably the centers of synthesis in the cells. The parathyroid glands produce parathyroid hormone (parathormone), which helps regulate calcium and phosphorus metabolism. There are reciprocal relations between the calcium and phosphorus concentrations in the blood. Calcium and phosphorus homeostasis is maintained by the influence of parathyroid hormone on bone tissue and on the kidneys. An excess of the hormone causes demineralization of the bone tissue and the excretion of calcium and phosphorus from the body. Excess phosphorus is excreted by the kidneys. Softening of bones and their eventual spontaneous fracture occur in hyperparathyroidism; tooth development is slowed in hypoparathyroidism. The administration of parathyroid hormone relieves the symptoms of parathyroid deficiency. Removal of the glands results in convulsions (tetany), caused by the sharp decrease in the blood’s calcium concentration (from 9–11 to 4.5–5 mg percent). Blood phosphorus increases at the same time. Attacks of tetany may occur in animals with normal parathyroids when their food contains insufficient calcium. The size and functional condition of the parathyroids vary with the blood calcium level. REFERENCES Leites, S. M., and N. N. Lapteva. Ocherki po patofiziologii obmena veshchestv i endokrinnoi sistemy. Moscow, 1967. Eskin, I. A. Osnovy fiziologii endokrinnykh zhelez. Moscow, 1968. Clegg, P., and A. Clegg. Gormony, kletki, organizm. Moscow, 1971. (Translated from English.) V. M. SAMSONOVA parathyroid glands 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 glands Four, yellow, bean-shaped bodies, each about 0.5 cm long, lying behind the THYROID GLAND, usually embedded in its capsule. The parathyroids secrete a hormone, parathyroid hormone (parathormone or PTH), into the blood if the level of calcium in the blood drops. This hormone promotes the release of calcium from the bones, controls loss in the urine and increases absorption from the intestine, thus correcting the deficiency in the blood. Maintenance of accurate levels of blood calcium is more important, physiologically, than the strength of the bones. Secretion of abnormal quantities of PTH from a parathyroid tumour can lead to bone softening. Underaction of the parathyroids causes a dangerous drop in the blood calcium. Sandström, Ivor V., swedish anatomist, 1852-1889. Sandström bodies - Synonym(s): parathyroid glands
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