Phosphates are a series of chemical compounds that contain phosphorus. For example, they are found in adenosine triphosphate (ATP) – the primary energy source in the body. Increased phosphate concentration in the blood is associated with kidney disorders, among other things.
What are phosphates?
Phosphates are formed from orthophosphoric acid. As salts of orthophosphoric acid, they consist of both positively and negatively charged ions (cations and anions). In contrast, the esters of orthophosphoric acid are formed from a chemical reaction of the acid with an alcohol. Water splits off in the process. Both salts and esters of orthophosphoric acid occur in the organism only in oxidized form. The compounds are poorly soluble in water. Phosphates can be divided into three groups. The primary or dihydrogen phosphates have two hydrogen atoms. In contrast, the secondary phosphates or hydrogen phosphates have only one hydrogen atom per phosphate compound. The tertiary phosphates do not have any hydrogen atoms at all. However, these three variants are not the only possible subdivisions. In addition, phosphates can exist as condensates. These are formed with the elimination of water. At the end of the biochemical reaction, diphosphoric acid is formed, which owes its name to the two phosphorus particles.
Function, effect and tasks
Phosphates are vital to the human body – but all other living things depend on the chemical compound as well. As an ester of phosphoric acid, it forms a component of nucleic acids. The nucleic acids make up deoxyribonucleic acid, or DNA for short; it stores all hereditary information and controls the metabolism of the cells. Human DNA consists of the four nucleic acids adenine, thymine, guanine and cytosine, whereby adenine and thymine as well as guanine and cytosine can form a so-called base pair. A long chain of the various nucleic acids forms a specific code that the cells can translate into protein chains and read out in this way. These protein chains can represent messenger substances or building blocks for microscopic cell structures. In addition, phosphates are significantly involved in energy metabolism. As adenosine triphosphate (ATP), they form the primary energy carrier within the organism. ATP consists of three phosphates, a sugar molecule (ribose) and an adenine residue. The cleavage of a phosphate releases chemically bound energy. What remains is a compound consisting of two phosphates: Adenosine diphosphate. Cells use the released energy for almost all processes. Muscles also depend on ATP. Their fibers consist of fine filaments that push into each other during contraction, thereby shortening the muscle. ATP has a softening effect in this process: it disengages the fine fibers from each other, thereby allowing them to move again. Rigor mortis is a result of the lack of ATP.
Formation, occurrence, properties, and optimal values
The optimal value for phosphate in blood is 0.84-1.45 mmol/l. This range represents the general frame of reference. In some circumstances, these reference values may not be applicable: Depending on the test used, the examining laboratory may issue other reference values, which are then valid. On average, a person consumes about 1000-1200 mg of phosphate. However, the digestive system does not absorb the full amount of this, but only about 800 mg. The intracellular space stores most of the phosphates that come from food. Intracellular space is how biology summarizes all the spaces in cells. However, the cells do not metabolize the phosphates directly, but initially only absorb them. The intracellular space holds 70% of the phosphates. Another 29% is located in the bone. The phosphates are stored there in the so-called mineralization front, where they are available to the body for further use and thus do not become a permanent part of the bone. In the blood circulate the remaining 1% of phosphates. Medicine summarizes the phosphate stores in the intracellular space, bone and blood as the phosphate pool. The phosphate pool forms the totality of phosphates in the body that are exchangeable. Moreover, the bones can bind calcium phosphate permanently; they release it only in severe deficiency states, which can lead to osteoporosis (bone loss).
Diseases and disorders
An abnormally elevated phosphate level manifests clinically as hyperphosphatemia. A blood test may confirm the finding. Hyperphosphatemia may be due to a variety of causes. In addition to an unusually high intake of phosphates through food, kidney failure, kidney disorders, and tissue destruction are possible triggers. The kidneys play an important role in regulating the amount of phosphate in the body. They filter urinary substances, which include phosphates, from the blood and excrete them in the urine. In this way, they can regulate an intake of up to 4000 mg/d. Higher amounts can trigger hyperphosphatemia. In acute hyperphosphatemia, the phosphate level increases abruptly. In this case, the disease manifests itself in symptoms such as diarrhea, nausea, vomiting, loss of appetite, muscle cramps, cardiac arrhythmias, seizures and circulatory collapse. There is also a risk of sudden cardiac death. Secondarily, hypocalcemia may develop, in which blood calcium levels fall below 2.2 mmol/l. Possible symptoms include paresthesias and pawing of the arms. Hypocalcemia is based on the fact that during acute hyperphosphatemia, calcium precipitates in the tissues and is therefore no longer bound in the blood. Chronic hyperphosphatemia may have its origin in renal failure. In this case, the organs are no longer able to regulate the amount of phosphate in the blood. Often, other consequences of kidney failure occur in addition to chronic hyperphosphatemia. It increases the risk of heart attack, stroke and vascular occlusion. Dialysis treatment may be considered for therapy.
