<P> When red cells reach the end of their life due to aging or defects , they are removed from the circulation by the phagocytic activity of macrophages in the spleen or the liver or hemolyze within the circulation . Free hemoglobin is then cleared from the circulation via the hemoglobin transporter CD163 , which is exclusively expressed on monocytes or macrophages . Within these cells the hemoglobin molecule is broken up , and the iron gets recycled . This process also produces one molecule of carbon monoxide for every molecule of heme degraded . Heme degradation is one of the few natural sources of carbon monoxide in the human body , and is responsible for the normal blood levels of carbon monoxide even in people breathing pure air . The other major final product of heme degradation is bilirubin . Increased levels of this chemical are detected in the blood if red cells are being destroyed more rapidly than usual . Improperly degraded hemoglobin protein or hemoglobin that has been released from the blood cells too rapidly can clog small blood vessels , especially the delicate blood filtering vessels of the kidneys , causing kidney damage . Iron is removed from heme and salvaged for later use , it is stored as hemosiderin or ferritin in tissues and transported in plasma by beta globulins as transferrins . When the porphyrin ring is broken up , the fragments are normally secreted as a yellow pigment called bilirubin , which is secreted into the intestines as bile . Intestines metabolise bilirubin into urobilinogen . Urobilinogen leaves the body in faeces , in a pigment called stercobilin . Globulin is metabolised into amino acids that are then released into circulation . </P>
<P> When red cells reach the end of their life due to aging or defects , they are removed from the circulation by the phagocytic activity of macrophages in the spleen or the liver or hemolyze within the circulation . Free hemoglobin is then cleared from the circulation via the hemoglobin transporter CD163 , which is exclusively expressed on monocytes or macrophages . Within these cells the hemoglobin molecule is broken up , and the iron gets recycled . This process also produces one molecule of carbon monoxide for every molecule of heme degraded . Heme degradation is one of the few natural sources of carbon monoxide in the human body , and is responsible for the normal blood levels of carbon monoxide even in people breathing pure air . The other major final product of heme degradation is bilirubin . Increased levels of this chemical are detected in the blood if red cells are being destroyed more rapidly than usual . Improperly degraded hemoglobin protein or hemoglobin that has been released from the blood cells too rapidly can clog small blood vessels , especially the delicate blood filtering vessels of the kidneys , causing kidney damage . Iron is removed from heme and salvaged for later use , it is stored as hemosiderin or ferritin in tissues and transported in plasma by beta globulins as transferrins . When the porphyrin ring is broken up , the fragments are normally secreted as a yellow pigment called bilirubin , which is secreted into the intestines as bile . Intestines metabolise bilirubin into urobilinogen . Urobilinogen leaves the body in faeces , in a pigment called stercobilin . Globulin is metabolised into amino acids that are then released into circulation . </P>
portion of hemoglobin associated with the production of bilirubin
portion of hemoglobin associated with the production of bilirubin
heme
heme