Figure 2.

Processes involved in N balance in the liver.

Notes: In periportal hepatocytes, amino acids (including glutamine) are metabolized to NH₃ and CO₂ in the mitochondria, and all this NH₃ is captured and converted to urea by the urea cycle. About half of the NH₃ removed by the liver diffuses to the urea cycle and is converted to urea. In perivenous hepatocytes, the other half of the NH₃ that is removed is stoichiometrically converted to glutamine by glutamine synthetase (GLS), with the glutamine leaving in the hepatic vein.