Phosphorus absorption in gastrointestinal tract

The level of phosphorus in the blood is regulated by parathyroid gland, which interacts with vitamin D to control the amount of phosphorus absorbed, the amount retained by the kidneys and the amount either released from or deposited in bone.

Phosphorus absorption occurs throughout the small intestine, but primarily in the duodenum and jejunum with minimal absorption occurring in the ileum. Between 60% to 70% of dietary phosphorus is absorbed by the gastrointestinal tract. Unlike calcium the intestinal absorption of phosphorus is not controlled according to the body needs.

Phosphorus absorption occurs by two processes:
*Saturable, carrier-mediated, active transport
*Diffusion

Due to typically inorganic phosphate concentrations, the absorption of phosphate is thought to occur primarily by passive diffusion.

Maintenance of the phosphate balance is achieved largely thorough renal excretion.

Vitamin D sterols promote intestinal phosphorus absorption by increasing sodium-phosphate co-transport across the apical brush-border membrane. Phosphorus is quickly absorbed from intestine and into the blood, appearing in the blood within about an hour after ingestion.

Although some phosphorus is lost in gastrointestinal secretions and as a result of the sloughing of intestinal epithelial cells, the net input of phosphorus into extracellular fluid from gastrointestinal tract is approximately 600 to 800 mg per day.

In healthy people the rate at which phosphorus is absorbed from the gastrointestinal tract and excreted via the kidneys is equal, maintaining total body phosphorus at a steady level.
Phosphorus absorption in gastrointestinal tract