phosphatehandling

Phosphate handling is the physiological regulation of inorganic phosphate (PO4^3−) across intestinal absorption, renal excretion, and bone buffering to maintain phosphate homeostasis. Phosphate is essential for energy metabolism, nucleic acids, and cell membranes; most body phosphate is stored in bone, with smaller pools in soft tissue and extracellular fluid.

Dietary phosphate is absorbed in the small intestine, with absorption efficiency influenced by vitamin D status. In the kidney, filtration is followed by proximal tubular reabsorption via sodium-phosphate cotransporters, primarily NaPi-IIa (SLC34A1) and NaPi-IIc (SLC34A3).

Renal phosphate reabsorption is regulated by hormones such that parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) promote phosphate excretion, while vitamin D promotes intestinal uptake and, indirectly, renal reabsorption. The balance is described by the tubular maximum reabsorption of phosphate (TmP/GFR) and the fractional excretion of phosphate (FEPO4) used in clinical assessment.

Bone serves as a dynamic reservoir, buffering changes in serum phosphate in response to hormonal signals, helping stabilize circulating phosphate levels.

Dysregulation occurs in chronic kidney disease, where reduced excretion leads to hyperphosphatemia and vascular calcification risk, and in conditions causing phosphate loss or malabsorption, leading to hypophosphatemia. Management may include dietary modification, phosphate binders, vitamin D analogs, and therapies targeting PTH or FGF23 signaling.