endocrine and metabolic disorders
Overview of Disorders of Calcium Concentration
Regulation of Calcium Metabolism
The metabolism of calcium and of phosphate (see Overview of Disorders of Phosphate Concentration ) is intimately related. The regulation of both calcium and phosphate balance is greatly influenced by concentrations of circulating PTH, ]), especially in patients with Chronic Kidney Disease . is secreted by the Overview of Parathyroid Function . It has several actions, but perhaps the most important is to defend against Renal calcium excretion generally parallels sodium excretion and is influenced by many of the same factors that govern sodium transport in the proximal tubule. However, PTH enhances distal tubular calcium reabsorption independently of sodium. PTH also decreases renal phosphate reabsorption and thus increases renal phosphate losses. Renal phosphate loss prevents the solubility product of calcium and phosphate from being exceeded in plasma as calcium concentrations rise in response to PTH. PTH also increases serum calcium by stimulating conversion of Vitamin D Deficiency and Dependency to its most active form, Radioimmunoassays for the intact PTH molecule are the recommended way to test for PTH. Second-generation assays for intact PTH are available. These tests measure bioavailable PTH or complete PTH. They give values equal to 50 to 60% of those obtained with the older assay. Both types of assays can be used for diagnosing Primary hyperparathyroidism or monitoring PTH increases urinary cAMP. Sometimes total or nephrogenous cAMP excretion is measured in diagnosis of Pseudohypoparathyroidism . Calcitoninis secreted by the thyroid parafollicular cells (C cells).Calcitonintends to lower serum calcium concentration by enhancing cellular uptake, renal excretion, and bone formation. The effects ofcalcitoninon bone metabolism are much weaker than those of either PTH orvitamin D. 