Concentration 2.5-4.5 mg/dL and reflects serum inorganic phosphorus.
Levels regulated by the kidneys, bones and intestines.
Phosphorus is regulated simultaneously with calcium by Vitamin D3, PTH, and calcitonin.
The kidneys are the primary avenue of phosphorus excretion.
Primary mechanism of renal handling is the Na/PO4 co-transporter which is located in the apical tubular membrane with expression mediated by serum parathyroid hormone.
Renal phosphate handling occurs in the proximal tubule where 70-80% of filtered phosphate is recovered by the two principal NaPi-IIa and NaPi-IIc phosphate transporters.
Parathyroid hormone and calcitonin increases renal elimination.
Anabolism and phosphorus deficiency decreases renal elimination.
Majority of phosphorus is in the extracellular space and exists as inorganic phosphate ions.
Phosphorus is an extracellular fluid cation.
Phosphorus intake is essential to normal bone development and mineralization.
Although most adults consume more than the recommended 700 mg/day of phosphorus, 10–15% of older adults have inadequate phosphorus intake.
Eighty-five percent of the total body phosphorus is in the bones and teeth in the form of hydroxyapatite.
The soft tissues contain the remaining 15% of phosphorus.
Levels regulated by a number of hormones that also control calcium metabolism.
Hypophosphatemia in refeeding syndrome results from transcellular shift in phosphate and increased tissue requirements during anabolism.
Dietary phosphorous mainly in dairy products, red meat, poultry and eggs.
Absorbed in the jejunum.
Average storage form in adult is 700 gms, with most residing within bone (75%) and muscle, with the remainder in enzyme systems such as 2,3 diphosphoglycerate, nuclear proteins and ATP.
Increased intestinal absorption with decreased calcium levels, hyperacidity of the intestine and via Vitamin D.
Phosphorus imbalance may result due to three processes: dietary intake, gastrointestinal disorders, and excretion by the kidneys.
Average adult consumes 800-1000 mg daily
Predominantly excreted by the kidneys.
Filtered at the glomerulus with 75% reclaimed by the proximal and distal convoluted renal tubules.