What is the lifespan of erythrocytes?

• A. About 60 days
• B. About 180 days
• C. About 120 days
• D. About 30 days

Answer: (C)

Red blood cells live about 120 days because they lack nuclei and most organelles, so they can’t repair damage or synthesize new proteins. As they circulate, they gradually become less flexible and more prone to damage. Older cells are recognized and removed by macrophages in the spleen (and to some extent the liver) through a process called extravascular hemolysis. The body recycles what it can: iron is returned to the bone marrow for new hemoglobin, and bilirubin from heme is processed by the liver and excreted. To keep a steady supply of red blood cells, erythropoiesis in the bone marrow is driven by erythropoietin. That combination explains why the typical lifespan is about 120 days. Shorter timeframes like 60 or 30 days would imply far more rapid turnover than is observed, and 180 days exceeds the usual lifespan of circulating erythrocytes.