Ammonia's Role in Biological Systems and Human Disease
Ammonia is an important source of nitrogen for living systems. Although atmospheric nitrogen abounds (more than 75%), few living creatures are capable of using this nitrogen. Nitrogen is required for the synthesis of amino acids, which are the building blocks of protein. Some plants rely on ammonia and other nitrogenous wastes incorporated into the soil by decaying matter. Others, such as nitrogen-fixing legumes, benefit from symbiotic relationships with rhizobia that create ammonia from atmospheric nitrogen.
Ammonia also plays a role in both normal and abnormal animal physiology. It is biosynthesised through normal amino acid metabolism and is toxic in high concentrations. The liver converts ammonia to urea through a series of reactions known as the urea cycle. Liver dysfunction, such as that seen in cirrhosis, may lead to elevated amounts of ammonia in the blood (hyperammonemia). Likewise, defects in the enzymes responsible for the urea cycle, such as ornithine transcarbamylase, lead to hyperammonemia. Hyperammonemia contributes to the confusion and coma of hepatic encephalopathy, as well as the neurologic disease common in people with urea cycle defects and organic acidurias.
Ammonia is important for normal animal acid/base balance. After formation of ammonium from glutamine, α-ketoglutarate may be degraded to produce two molecules of bicarbonate, which are then available as buffers for dietary acids. Ammonium is excreted in the urine, resulting in net acid loss. Ammonia may itself diffuse across the renal tubules, combine with a hydrogen ion, and thus allow for further acid excretion.
Read more about this topic: Ammonia
Famous quotes containing the words role, biological, systems, human and/or disease:
“Whatever we’re doing, whoever we are, it isn’t enough. . . . Little wonder we have trouble finding role models to guide us through these shoals. No one less than God Herself could be all the things we’d like to be to all the people we’d like to feel approval from.”
—Melinda M. Marshall (20th century)
“If the most significant characteristic of man is the complex of biological needs he shares with all members of his species, then the best lives for the writer to observe are those in which the role of natural necessity is clearest, namely, the lives of the very poor.”
—W.H. (Wystan Hugh)
“The skylines lit up at dead of night, the air- conditioning systems cooling empty hotels in the desert and artificial light in the middle of the day all have something both demented and admirable about them. The mindless luxury of a rich civilization, and yet of a civilization perhaps as scared to see the lights go out as was the hunter in his primitive night.”
—Jean Baudrillard (b. 1929)
“The crime of book purging is that it involves a rejection of the word. For the word is never absolute truth, but only man’s frail and human effort to approach the truth. To reject the word is to reject the human search.”
—Max Lerner (b. 1902)
“The fantasies inspired by TB in the last century, by cancer now, are responses to a disease thought to be intractable and capricious—that is, a disease not understood—in an era in which medicine’s central premise is that all diseases can be cured.”
—Susan Sontag (b. 1933)