Regulation of phosphorus balance

Where is phosphorous found in the body?

Phosphate homeostasis

Plasma phosphate is determined by
(1) intestinal absorption
(2) storage in bone
(3) excretion by the kidneys

Where is phosphate reabsorbed?

primarily by the proximal tubule

What stimulates PTH secretion and what does it do?

Hypocalcaemia

• stimulates bone resorption

• increases urinary Pi excretion

• decreases urinary Ca ++ excretion

• stimulates production of calcitriol

** Increases plasma [Ca ++ ] while having little effect on the plasma [Pi ]

What stimulates calcitriol secretion and what does it do?

Hypocalcaemia (via PTH) and hypophosphatemia

• stimulates Ca ++ and Pi absorption by the intestine

• acts with PTH to release Ca ++ and Pi from the bone

• decreases Ca ++ excretion by the kidneys

** Increase the plasma [Ca ++ ] and [Pi ]

What increases PCT reabsorption?

Metabolic alkalosis and phosphate depletion

What decreases PCT reabsorption?

PTH, FGF-23, metabolic acidosis, phosphate loading

Main cause of Hypophosphatemia

reduced renal phosphate excretion

eg. acute renal failure