Phosphorus is a chemical element (Atomic Number 15).  In its pure form, it is very reactive and, as such, is usually found bound to other elements, particularly oxygen, in compounds.  In organic chemistry, phosphorus is a key element of DNARNAATP and cell membranes.  The average human body contains about 700g of phosphorus and excretes it in both urine and stool.  

There are some diseases that affect the metabolism of phosphorus in the human body.  When a body is malnourished and then re-nourished, the body will often draw phosphorus out of the blood and medical personnel must insure that it is replaced.  Very low levels of phosphorus will cause neurological symptoms, loss of muscle control and problems with the blood.  Conversely, too much phosphorus can cause diarrhea and calcification, as well as interference with the body's ability to process other vital minerals.  

Phosphorus at Wikipedia

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