Preksha Meditation & Human Health: 2.3.1.3 Life Span of RBCs

The life span of Red blood cells is approximately 120 days. After this duration RBCs become fragile and are removed from circulation by macrophages, knowns as "big eaters", are found in the liver, spleen, and red bone marrow. The old RBCs are phagocytized and digested by macrophages, and their iron component is returned to the blood to be returned to the red bone marrow to be used for the synthesis of new haemoglobin. Any excess amount of iron is stored in the liver. The iron and globin of RBCs are recycled over and over again. It is digested to its amino acids, which may then be used for the synthesis of new proteins. Another important constituent of the haemoglobin is the heme portion, which is never recycled and is a waste product. The heme is converted to bilirubin by macrophages. The liver removes bilirubin from circulation and excretes it into bile. Bile is than secreted by the liver into the duodenum and passes through the small intestine and colon to be eliminated through feces and gives feces their characteristic brown color. In the colon some bilirubin is changed to urobilinogen by the colon bacteria. Some urobilinogen may be absorbed into the blood, but it is changed to urobilin and excreted by the kidneys in urine. If bilirubin is not excreted properly, perhaps because of liver disease such as hepatitis, it remains in the blood. This may cause jaundice, a condition in which the whites of the eyes appear yellow. This yellow color may also be seen in the skin of light skinned people.