parathyroid hormone (PTH), a hormone secreted by the parathyroid glands that acts to maintain a constant concentration of calcium in the extracellular fluid. The hormone regulates absorption of calcium from the GI tract; mobilization of calcium from the bones; deposition of calcium in the bones; and excretion of calcium in the breast milk, feces, sweat, and urine. Surgical removal of the parathyroid glands, as may inadvertently occur in thyroidectomy, results in hypocalcemia, leading to anorexia, tetany, seizures, and death if not corrected. Normal parathyroid laboratory findings are less than 2000 pg/mL. See also hypoparathyroidism.
