Factors phosphate homeostasis

Three hormones serve as the principal regulators of calcium and phosphate homeostasis parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and the steroid vitamin D (Figure 42-2). Vitamin D is a prohormone rather than a true hormone, because it must be further metabolized to gain biologic activity. PTH stimulates the production of the active metabolite of vitamin D, l,25(OH)2D. l,25(OH)2D, on the other hand, suppresses the production of PTH. l,25(OH)2D stimulates the intestinal absorption of calcium and phosphate. l,25(OH)2D and PTH promote both bone formation and resorption in part by stimulating the proliferation and differentiation of osteoblasts and osteoclasts. Both... 

Factors That Can Influence Calcium and Phosphate Homeostasis... 

Four primary factors influencing calcium and phosphate homeostasis are diet, vitamin D and its metabolites, PTH, and calcitonin. Table 37-1 lists other hormones known to... 

As mentioned above, many transcription factors are not always active. Rather the activity of transcription factors is often achieved by induced reversible modification. Most frequently is the addition of phosphate groups (phosphorylation) to Ser, Thr, or Tyr residues. For the AP-1 component c-Jun the phosphorylation at Ser63 and Ser73 enhances activity when cells are subjected to stress, e.g. radiation. Phosphorylation is, however, dispensable for c-Jun-dqDendent tissue homeostasis in the liver, indicating that certain activities do not require the regulatory enhancement. Jun-N-teiminal kinase and a kinase called RSK or p38 catalyze the phosphorylation of AP-1. 

The main function of vitamin D is in the control of calcium homeostasis (section 11.15.1) and, in turn, vitamin D metabolism is regulated, at the level of 1- or 24-hydroxylation, by factors that respond to plasma concentrations of calcium and phosphate ... 

---