The parathyroids are usually four tiny yellowish-brown glands, each about the size of a grain of rice, on the back of the thyroid lobes. They make parathyroid hormone, the main hormone that keeps blood calcium in a tight normal range. The superior pair develop from the fourth pharyngeal pouch and the inferior pair from the third, which is why the lower glands are more variable in position.
| Location | Posterior surface of the thyroid lobes, usually two on each side; superior glands near the cricothyroid junction, inferior glands near the lower poles close to the inferior thyroid artery |
|---|---|
| Secretes |
|
| Blood Supply | Inferior thyroid artery (main supply); Superior thyroid artery |
| Venous drainage | |
| Lymphatic drainage |
Releases PTH when blood calcium falls; PTH raises calcium by releasing it from bone, increasing reabsorption in the kidney and activating vitamin D to improve absorption from the gut.
Primary hyperparathyroidism, usually from a single adenoma, is a common cause of raised calcium and presents with kidney stones, bone loss, abdominal pain and low mood ('stones, bones, groans and moans'). Injury to or removal of the glands during thyroid surgery causes low calcium with tingling around the mouth and muscle cramps. Inferior glands may sit low in the neck or in the thymus.
Overproduction of PTH, usually by a single adenoma, causing high calcium, kidney stones and osteoporosis.
Low PTH and calcium after thyroid or neck surgery damages the glands or their blood supply, causing tingling, cramps and tetany.
Glandular overactivity driven by low calcium or vitamin D, most often in chronic kidney disease.
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