Parathyroid Gland

E. Parathyroid gland : The four parathyroid glands, named superior and inferior on each side, sit on the posterior surface of the thyroid's two lobes, their cells arranged in a compact mass. They secrete the peptide hormone parathormone (PTH, also called Collip's hormone), which regulates the balance of calcium and phosphate between blood and other tissues -- raising blood calcium by mobilising calcium out of bone, increasing its absorption from the digestive tract, and reducing its loss in urine. Parathormone secretion is itself controlled by feedback from blood calcium level, and, together with calcitonin (from the thyroid), the two hormones form an antagonistic pair -- much like insulin and glucagon -- that jointly holds blood calcium and phosphate steady.

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