Phosphate what is it?

Phosphate is the most abundant intracellular anion.

 One hundredth of the body’s mass is made up of phosphate. Most of this is stored as hydroxyapetite crystals in the bone matrix. Only 15 % is metabolically active, and 1% is present in the blood. Phosphorous is the most abundant intracellular anion, it’s concentration is approximately 100mmol/l. The intracellular concentration of phosphorous is 100 times greater than the plasma concentration.  This figure is somewhat misleading, nonetheless, as the multiple functions of the anion ensure that only a small amount of it is in the free (inorganic) form. The average diet provides 800-1400 mg of phosphorous daily. Of this, 70% is absorbed through the gut, mainly by passive transport, but there is also some active transport, stimulated by vitamin D metabolites. Normal plasma range is between 2.8 and 4.5 mg/dl. The main organ of regulation of phosphate is the kidney. Phosphorous is filtered by the nephron, and mostly reabsorbed in the proximal tubule in a cotransport with sodium. This cotransport is regulated by phosphorous intake (i.e. serum phosphorous levels) and parathyroid hormone (PTH). PTH inhibits the co-transport mechanism, and increases urinary excretion of phosphorous.

In the blood, phosphate is present in multiple forms – as phospholipids, as PO4^3-, as H2PO4^- and HOP4^2-.

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