In addition, the liver filters out waste substances produced by the body. When red blood cells die, they release haemoglobin, the compound that enables them to carry oxygen. Cells in the liver and other organs break down haemoglobin into several substances, including iron and a reddish-yellow pigment called bilirubin. The liver discharges bilirubin in bile. It stores iron for use in producing new red blood cells.
The liver also rids the body of ammonia, a poisonous waste formed when amino acids are changed to other compounds in the liver. The liver converts the ammonia to urea, which is nonpoisonous. The urea is eventually discharged in urine.