The surgically stressed state is characterized by an elevation in protein turnover (i.e., protein synthesis and degradation), release of amino acids into circulation, urinary nitrogen losses, and impaired uptake of amino acids in skeletal tissue. Lean tissue is catabolized, releasing amino acids into circulation (including glutamine, alanine, and the branched chain amino acids [BCAAs]), while hepatic amino acid uptake is enhanced. This allows for reprioritization of protein synthesis to acute phase reactants and the production of glucose via gluconeogenesis. Glutamine (Glu) and alanine (Ala) account for the majority of the amino acid efflux from peripheral tissues and are readily extracted from circulation by the liver. The excess nitrogen is converted in the liver to urea by combining ammonia (NH₃) with CO₂ (carbon dioxide). Urea is then released into circulation, traveling to the kidneys, where it can be filtered into urine. The BCAAs undergo irreversible degradation in skeletal tissue, in part for synthesis of glutamine and alanine, which reduces availability of these indispensable amino acids for reutilization in protein synthesis. Collectively, these metabolic changes promote whole body protein catabolism.