Explain why arginine is classified as essential even though we make it in the urea cycle.

Arginine is classified as semi-essential or conditionally essential amino acid, which means it can be synthesized by the human body from glutamine via citrulline (in the urea cycle), but under certain conditions (illness, the stress of the body or immature individuals for example) might not be able to be produced. Dietary intake is the primary contributor to arginine levels since the rate of arginine synthesis in the body does not increase to compensate for depletion or inadequate supply. The main sources of arginine include seeds like grains, beans, and nuts, meat, dairy products and eggs.