ABSTRACT
Phosphorus is one of the most important inorganic elements, second only to calcium in abundance in the human body. In humans, approximately 85% of the total body phosphorus is in bones, 14% in cells and soft tissues, and 1% in extracellular fluids. The phosphorus contained in bone is in the mineral phase as inorganic orthophosphate and small amounts of inorganic phosphate. In soft tissue and cell membranes, phosphorus exists mainly as phosphate esters and to a lesser extent as phosphoproteins and free phosphate ions. In extracellular fluid, about one tenth of the phosphorus content is bound to proteins, one third is complexed to sodium, calcium, and magnesium, and the remainder is present as inorganic phosphate. In biological systems, phosphorus is present as phosphate, and these two terms are used interchangeably in this chapter.
