Osteocyte phosphate sensing
Sensor / first step · Osteocyte / osteoblast
Osteocytes and osteoblasts are the skeleton's phosphate sensor. A phosphate load, a rise in calcitriol or a rise in PTH increases their secretion of FGF23, the principal phosphaturic hormone.
Traced from the start
- Phosphate load and hyperphosphataemia
- Osteocyte phosphate sensing
Detail
- Secreted by
- Osteocytes and osteoblasts, not by the parathyroid or the kidney
- Stimulated by
- Dietary phosphate load and hyperphosphataemia, calcitriol, PTH, and iron deficiency through altered processing
- Processing
- Intact FGF23 is the active molecule; PHEX and furin-like proteases determine how much escapes cleavage
When it goes wrong
PHEX mutation causing X-linked hypophosphataemic rickets
Excess intact FGF23: renal phosphate wasting with a low phosphate, inappropriately normal or low calcitriol, normal calcium and PTH, and rickets that will not respond to plain vitamin D; treated with phosphate and calcitriol, or with burosumab
Phosphaturic mesenchymal tumour (tumour-induced osteomalacia)
Acquired FGF23 excess: adult-onset hypophosphataemic osteomalacia with bone pain and proximal myopathy, cured by resecting the tumour
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