Paratyreoide

Paratyreoide, or parathyroid glands, are four small endocrine glands located on the posterior surface of the thyroid gland in the neck. They typically consist of chief cells and oxyphil cells and arise during development from the third and fourth pharyngeal pouches. In some individuals there are more or fewer glands, and ectopic glands may be found along the neck or within the mediastinum.

The glands secrete parathyroid hormone (PTH), the principal regulator of calcium and phosphate homeostasis. PTH raises serum calcium by stimulating bone resorption, increasing renal calcium reabsorption, and promoting production of active vitamin D (calcitriol), which enhances intestinal calcium absorption. It simultaneously lowers serum phosphate by reducing renal phosphate reabsorption.

PTH secretion is tightly governed by blood calcium levels via calcium-sensing receptors on parathyroid cells. Low calcium stimulates PTH release; high calcium inhibits it. Vitamin D status and renal function also influence PTH secretion.

Disorders include hyperparathyroidism and hypoparathyroidism. Primary hyperparathyroidism is usually caused by a benign adenoma or multiglandular hyperplasia; secondary hyperparathyroidism results from chronic hypocalcemia, most commonly due to kidney disease; tertiary hyperparathyroidism refers to autonomous PTH secretion after long-standing secondary disease. Hypoparathyroidism, often after thyroid or neck surgery, causes hypocalcemia and neuromuscular symptoms managed with calcium and active vitamin D.

Diagnosis and localization of abnormal glands may involve ultrasound, nuclear medicine sestamibi scans, and CT or MRI. Treatment depends on cause and may include surgical removal of affected glands, medical management to control calcium (and phosphate) levels, and monitoring for complications. Ectopic or supernumerary glands can complicate localization.