The grouping of four small glands, about 5 mm in diameter, which lie to the side of and behind the THYROID GLAND. These glands regulate the metabolism of calcium and of phosphorus. If for any reason there is a de?ciency of the secretion of the parathyroid glands, the amount of calcium in the blood falls too low and the amount of phosphorus increases. The result is the condition known as TETANY characterised by restlessness and muscle spasms – sometimes severe. The condition is checked by the injection of calcium gluconate, which causes an increase in the amount of calcium in the blood.
The most common cause of this condition (hypoparathyroidism) is accidental injury to or removal of the glands during the operation of thyroidectomy for the treatment of Graves’ disease (see THYROID GLAND, DISEASES OF – Thyrotoxicosis). If there is over-production of the parathyroids, there will be an increase of calcium in the blood: this extra calcium is drawn from the bones, causing cysts to form with resulting bone fragility. This cystic disease of bone is known as OSTEITIS FIBROSA CYSTICA. Tumours of the parathyroid glands result in this overactivity of the parathyroid hormone, and the resulting increase in the amount of calcium in the blood leads to the formation of stones in the kidneys. The only available treatment is surgical removal of the tumour. Increased activity of the parathyroid glands, or hyperparathyroidism, may cause stones in the kidneys. (See KIDNEYS, DISEASES OF.)
These are several minute glandular masses embedded in the lower edge of the thyroid gland. They produce Parathyroid Hormone (PTH), part of the calcium-phosphorus control system. Calcium levels in the blood MUST be within a narrow band of safety. If free calcium drops too low, PTH acts on the kidneys and blocks calcium loss in urine, amplifies calcium absorption into the portal blood (from food and from submucosal storage) and stimulates release of calcium from bone storage. When levels are back up, the hormone backs off. Oddly enough, the thyroid gland secretes its virtual antagonist, calcitonin, which, when calcium levels are too high, stimulates the urine excretion, bone retention and digestive resistance to calcium, and when the blood levels drop, recedes. The body finds calcium levels to be so critical that it has in place TWO separate, mutually antagonistic negative feedback systems,,,like a binary star system. (Be thankful I didn’t bring in the calcium maintenance of minerocortical steroid hormones or vasopressin)... parathyroids
(PTH-RP) a protein that is secreted by certain malignant tumours and is the main cause of malignant *hypercalcaemia. PTH-RP, which has effects similar to *parathyroid hormone, stimulates generalized bone resorption and excessive calcium reabsorption in the kidney tubules. It is most commonly produced by lung tumours, squamous-cell carcinomas of other organs, melanomas, and tumours of the breast, liver, pancreas, bladder, and prostate.... parathyroid hormone-related protein
(in *nuclear medicine) a scan that can help to localize the site of a parathyroid adenoma before surgical removal, to treat primary *hyperparathyroidism. The tracer is technetium-99m-labelled sestamibi (a small protein), which is selectively absorbed by overactive parathyroid glands.... sestamibi parathyroid scan
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