ureacyklen

The ureacyklen, also known as the urea cycle, is a metabolic pathway that occurs in the liver of ureotelic animals. Its primary function is to convert excess nitrogen, primarily in the form of ammonia, into urea, a less toxic compound that can be excreted from the body. This process is crucial for preventing ammonia toxicity, which can have severe neurological consequences.

The urea cycle consists of five enzymatic steps. It begins in the mitochondria with the condensation of ammonia and carbon dioxide to form carbamoyl phosphate. This is then transported to the cytoplasm and combined with ornithine to form citrulline. Citrulline then reacts with aspartate to produce argininosuccinate. Argininosuccinate is cleaved to form fumarate and arginine. Finally, arginine is hydrolyzed by arginase to yield urea and ornithine, which is then recycled back into the cycle.

Disruptions in the urea cycle can lead to various urea cycle disorders, a group of genetic conditions characterized by the accumulation of ammonia in the blood. These disorders can manifest with symptoms ranging from mild to severe, including lethargy, vomiting, seizures, and intellectual disability. Diagnosis typically involves blood tests to measure ammonia levels and amino acid profiles, as well as genetic testing. Treatment strategies often include dietary modifications to reduce protein intake, medication to help remove excess nitrogen, and in severe cases, liver transplantation.