Phosphorus
The adult human body has about 700 grams of Phosphorous (P) which make about 1% of the body weight. The whole blood contains around 48 mg P per 100 ml which is chiefly present as inorganic phosphate, organic phosphate esters and lipid Phosphorous (P). The red blood cells contains more P than plasma and contain much more organic phosphate while the inorganic phosphate is equally distributed in cells and the plasma. The plasma inorganic P level normally is 3 to 4 mg per 100 ml in the adults. In children the plasma inorganic P level is higher than in adults and is 4 to 7 mg per 100 ml; this is due to the activity of the growth hormone. The plasma inorganic P occurs in 2 forms, NP4= and N2PO4; these two forms are present normally in a ratio of roidism while its level is increased in renal failure due to a decreased elimination by the kidneys.
Dietary sources of Phosphorus
Foods rich Calcium (Ca) are also generally rich in Phosphorus (P) and include milk (93 mg%), beans, cereals, egg yolk and meats. A large part of the vegetable P exists as phytates of Ca and Mg which are insoluble and are largely not absorbed. A disadvantage of the phytates is that they interfere with the absorption of Ca, zinc and iron.
Absorption of Phosphorus
The P ingested with food is absorbed in inorganic form. An optimum Ca:P ration is helpful in the absorption of both these minerals. Excess of one decreases absorption of both. Excess of iron salts also interfere with P absorption because of the formation and a lowered intestinal pH favor P absorption. Organic phosphates are no way superior to inorganic phosphates as therapeutic agents and the use of the former as the so-called nerve tonic is not justified.
Functions of Phosphorus in the Body
- P takes part in formation of bones and teeth. 80 to 85% of body P is in bones. The inorganic part of the bone is mainly in the form 3Ca3(PO4)2Ca(OH)2 with carbonates absorbed on it.
- P forms a part of high energy compounds such as ATP, UTP, etc.
- It is a constituent of nucleic acids, both DNA and RNA, which are of great importance from the standpoint of protein synthesis, viruses and heredity.
- It is a constituent of phospholipids such lecithins, cephalins, plasmalogens, etc.
- It is an important constituent of cell memberanes.
- Phosphates are the most abundant anions present with in tissue cells.
- The Plasma phosphate takes part in buffer action concerned with pH regulation because it occurs in 2 forms, i.e. HPO4= and H2PO4.
- Phosphates form ester with sugars, e.g. glucose-6-phosphate, fructose-6-phosphate, etc. which take part in carbohydrate metabolism.