A red blood cell lives about 120 days before it starts to disintegrate. The hemoglobin from disintegrated red blood cells breaks down into four parts: globin, protein, iron, and heme. Heme eventually reduces into an orange-yellow pigment called bilirubin. This waste product moves to the liver, where it becomes more soluble and is combined with bile; the excretory system then excretes it as feces and urine.

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