Parathyroid hormone (PTH)
Reviewer: Monika Roychowdhury, M.D. (see Reviewers page)
Revised: 16 February 2013, last major update January 2013
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.
● Release controlled by ionized calcium level with negative feedback system
● 84 amino acids, derived from cleavage of pre-pro PTH; biologic activity due to 34 amino acids at amino terminus; other portions are inert but may give false positives in detection systems
● Binding of PTH to its receptor stimulates cAMP and phosphatidylinositol diphosphate
● Note: PTH-related protein is rarely produced by benign lesions, (Am J Clin Pathol 1996;105:487)
Five major actions:
1) Activates and increases the number of osteoclasts, which mobilizes calcium from bone
2) Increases renal tubular reabsorption of calcium
3) Increases conversion of Vitamin D to active dihyoxy form in kidneys
4) Increases urinary phosphate excretion, which reduces calcium loss
5) Increases GI calcium absorption
Hypercalcemia of malignancy (breast, lung, kidney, myeloma) due to
(a) release of PTH-related protein, usually in advanced disease, or
(b) osteolytic metastases with local release of cytokines (IL-1, TNF-alpha)
End of Parathyroid gland > General > Parathyroid hormone (PTH)
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