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Overview of the Endocrine System

Author(s): Center for Educational Outreach, Baylor College of Medicine.

Parathyroid Glands

Calcium is a mineral, vital to the formation of bone and teeth, blood clotting, and proper functioning of the brain nerves and muscles. The four parathyroid glands embedded in the thyroid gland function in the homeostasis of calcium, secreting parathyroid hormone (PTH), which raises blood levels of calcium, an effect opposite to that produced by the thyroid hormone, calcitonin. (PTH and calcitonin balance each other’s effects and minimize fluctuations in blood calcium concentration.) Specifically, parathyroid hormone causes mineralized bone to decompose and release calcium into the blood. Specialized cells, called osteoclasts, actually break down the bone. Parathyroid hormone also stimulates the uptake of calcium through the renal tubules.