Parathyroid hormone (PTH) is secreted from the parathyroid glands in response to low blood calcium levels [1]. Calcium-sensing receptors on parathyroid cells detect decreases in circulating ionized calcium and trigger increased PTH synthesis and release [2][4]. PTH acts to restore calcium homeostasis by promoting calcium resorption from bone, calcium reabsorption in the kidneys, and calcitriol synthesis to increase intestinal calcium absorption [1][3].

Parathyroid secretion is also modulated by magnesium levels, with hypomagnesemia stimulating PTH release [4][5]. In addition, catecholamines like norepinephrine can inhibit PTH secretion through β-adrenergic receptors on parathyroid cells [6]. Parathyroid hyperplasia and adenomas can cause dysregulated, autonomous PTH secretion resulting in hypercalcemia [3][5]. Hypoparathyroidism leads to hypocalcemia due to insufficient PTH levels [1][6].