urea cycle

noun

: a sequence of metabolic reactions occurring in the liver by which ammonia is converted to urea

The urea cycle is made up of six enzymes that rid the body of nitrogen produced during the metabolism of amino acids in food. They convert it to urea, which is eliminated in urine. If the cycle does not work, toxic ammonia builds up in the body—a condition called hyperammonemia—leading to brain damage, coma and death.

—Thomas H. Maugh II, The Los Angeles Times