Phosphorus: Absorption and Transport

Phosphorus: Absorption and Transport
Among the inorganic elements, phosphorus is second only to calcium in abundance in the human body. Approximately 85% of the body’s phosphorus is in the skeleton, with the remainder associated with organic substances of soft tissue. In its soft tissue form, phosphorus exists principally as phosphate esters of a multitude of metabolites and in lesser amounts as phosphoproteins and free phosphate ions.

Dietary phosphorus occurs in both inorganic form as well as phospholipids. The relative amounts of inorganic and organic phosphorus vary with the type of diet. Cow’s milk phosphorus is 70% inorganic, whereas phosphorus of cereal and the soft tissues of animal; is largely combined organically. But regardless of its dietary form, most phosphate is absorbed in its inorganic form, since organically bound phosphate is promptly hydrolyzed enzymatically in the lumen of small intestine and released as inorganic phosphate. Much of this enzymatic activity is attributed to the action of alkaline phosphatase, which functions at the brush border of the enterocytes.

Phosphorus absorption in man occurs throughout the small intestine. Nearly 70% is absorbed at a normal intake and up to 90% when intake is low. Unlike calcium the intestinal absorption of phosphorus is not controlled according to the body needs. Maintenance of the phosphate balance is achieved largely thorough renal excretion. Although definitive studies on the relative importance of each small intestinal segment in phosphorus absorption apparently lacking, it is known that the duodenal/ jejunal region is particularly importance.
Phosphorus: Absorption and Transport