The nitrogen waste produced primarily from AMINO ACID metabolism. Ammonia is highly toxic to the nervous system and the brain. It may interfere with metabolic processes required for energy production in the brain. Normally the brain transforms ammonia into GLUTAMINE, a safe, neutral amino acid released into the bloodstream. Next, glutamine is absorbed by the intestine, which releases the ammonia for disposal by the LIVER. Normally the liver very efficiently metabolizes ammonia to UREA, the ultimate nontoxic waste product, via the UREA CYCLE to keep the level of ammonia in the blood at very low levels. Urea is excreted safely in urine. Ammonia is also produced in the intestinal tract by bacteria. Ammonia is absorbed by the intestine and transported directly via the portal vein to the liver for disposal. Liver disease, such as CIRRHOSIS, reduces urea production and leads to elevated blood levels of ammonia (ammonemia), which causes neurological abnormalities. Genetic defects in the ammoniadisposal mechanism of the urea cycle generally lead to brain damage.
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