Parathyroid Disorders.

Parathyroid hormone (PTH) is a peptide hormone that is the primary regulator of calcium concentrations in the bloodstream. PTH is released in response to a variety of signals, most importantly in response to low serum calcium concentrations. As a true hormone, it travels through the bloodstream to target tissues, primarily in the bone and kidney, where it has a variety of effects that serve to increase serum calcium, thus providing a correction for the original stimulus for release. PTHserves as an important regulator of bone turnover and indifferent settings canhave either anabolic or catabolic effects in bone. Although PTH can mobilize phosphorus and calcium in bone, it also increases phosphate excretion, resulting in a net lowering of phosphate concentrations in the bloodstream. Given its central role in this important homeostatic process, a number of disorders are caused by abnormalities of PTH function.