QS Study

Physiology of Phosphate

Phosphate is one of the most abundant minerals in the body, and its serum levels are regulated by a complex set of processes occurring in the intestine, skeleton, and kidneys. It is an organic compound of phosphoric acid in which the acid group is bound to nitrogen or a carboxyl group in a way that permits useful energy to be released.

Phosphate is found in –

  • ATP
  • cAMP
  • 3 – Diphosphughyorre Proteins.

Two form –

  • HPO4-2 is about 1.05 mmol/L
  • H2PO4 is about 0.26 mmol/L.

Organic phosphate:

  • Total plasma phosphorus 12 mg/dl,
  • 2/3 of it – in organic compounds,
  • 1/3 of it – as inorganic PO43- (Pi)
  • mostly in – PO43-, H2PO4, HPO4-2


Site – Duodenum and Small intestine.

Process – Active transport and Passive diffusion.

Rate –

  • Linearly proportionate to dietary intake
  • Increased by 1.25 – Dihydroxy Cholecalciferol

Fig: Calcium Homeostasis

Function – Maintaining physiological phosphate balance is of crucial biological importance for bone health.

  • Helps in formation of bone and teeth,
  • Helps to transport of energy in the metabolic foodstuff.
  • Phosphorylation and dephosphorylation of proteins are involved in the regulation of cell function.
  • It regulates blood pH.


Mainly in urine, small amount through faeces –

  • Decrease PO43- in plasma, no excretion.
  • Inecrease PO43- – conc. in plasma excretion.


  • 85% – 90% of the filtered Pi is reabsorbed.
  • Process – Active transport.
  • This active transport is powerfully inhibited by PTH.