The urea cycle converts toxic nitrogenous compounds to excretable urea in five biochemical reactions. It is also the source for endogenous arginine, ornithine and citrulline production. The process mainly takes place in the liver, partly in the mitochondria and partly in the cytoplasm of hepatocytes.
Because there is no alternative way to convert toxic nitrogenous compounds, defects in the enzymes or transporters can lead to several diseases (highlighted in pink). The diseases are characterized by hyperammonemia, respiratory alkalosis and encephalopathy. The severity of the disease depends on the severity of the defect and the place of the defect in the cycle. Severe forms usually onset in infancy, while mild forms can also present in adulthood.
This pathway is based on [Mew NA, et al. Urea cycle disorders overview (2003)](https://www.ncbi.nlm.nih.gov/books/NBK1217/).