When red blood cells are delivered from the bone marrow into the circulatory system, they normally circulate an average of 120 days before being destroyed.
When red blood cells burst and release their hemoglobin, the hemoglobin is phagocytized almost immediately by macrophages in many parts of the body, but especially by the Kupffer cells of the liver and macrophages of the spleen and bone marrow.
During the next few hours to days, the macrophages release iron from the hemoglobin and pass it back into the blood, to be carried by transferring either to the bone marrow for the production ofnew red blood cells or to the liver and other tissues for storage in the form of ferritin.
Most of the heme degradation in biological systems occurs in two different pathways: an enzymatic pathway that requires the heme oxygenase system; or a nonenzymatic pathway that requires the interaction with reactive oxygen species (ROS), reducing agents, or xenobiotics.
*In the enzymatic pathway, heme oxygynase catalyzes heme cleavage and subsequently releases the heme iron in the ferrous form, and in a specific manner it eliminates the carbon-methene bridge of heme as CO to form bilivedrin.
*In the non-enzymatic pathways, ROS such as superoxide (O2−), hydrogen peroxide (H2O2), and hypochlorous acid (HOCl) can mediate heme destruction unselectively at any position of the heme double bonds.
Destruction of hemoglobin 
