BIOS 4500 Lecture Notes - Lecture 6: Periosteum, Teriparatide, Osteoporosis
1 Dec 2016
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Document Summary
Hormone synthesis and degradation regulated according to physiological demand. Pth is synthesized continuously: gland stores little hormone, synthesis regulated at transcriptional and at posttranscriptional sites. Vit d and high levels of extracellular calcium downregulates transcription. As much as 90% of the hormone synthesized may be metabolized within the chief cells which is cleaved into fragments when plasma calcium concentrations are high. Stimulates bone formation when pth is administered in low doses and intermittently (anabolic activity) Promotes reabsorption of ca2+ at the distal nephron. Promotes hydroxylation and thus activation of vitamin d at the proximal tubule. Synthesis of pth regulated at both transcriptional and posttranscriptional sites: cyclic amp upregulates & vit d downregulates transcription; extracellular calcium stimulate cleavage & inhibits secretion. Pth-actions at bone: early response (within 1-2h) Activation of preformed osteoclasts already present on the surface (osteocytic. Widespread resorption of both mineral and organic components of osteoclastic matrix osteolysis). activity predominates (high sustained levels of pth are catabolic to bone)
