<Li> Hemoglobin SC disease--A compound heterozygous form with one sickle gene and another encoding Hemoglobin C . </Li> <Li> Hemoglobin Hopkins - 2 - A variant form of hemoglobin that is sometimes viewed in combination with Hemoglobin S to produce sickle cell disease . </Li> <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> Hemoglobin deficiency can be caused either by a decreased amount of hemoglobin molecules, as in anemia, or by decreased ability of each molecule to bind oxygen at the same partial pressure of oxygen . Hemoglobinopathies (genetic defects resulting in abnormal structure of the hemoglobin molecule) may cause both . In any case, hemoglobin deficiency decreases blood oxygen - carrying capacity . Hemoglobin deficiency is, in general, strictly distinguished from hypoxemia, defined as decreased partial pressure of oxygen in blood, although both are causes of hypoxia (insufficient oxygen supply to tissues). </P>

Portion of hemoglobin associated with the production of bilirubin