Which organ is primarily responsible for breaking down aged red blood cells?

• A. Lungs
• B. Liver
• C. Pancreas
• D. Spleen

Answer: (D)

The spleen is the primary site where old red blood cells are removed from circulation. In the red pulp, specialized macrophages continually monitor passing erythrocytes and engulf those that are aged or damaged, a process that makes the red blood cells less flexible and prone to being trapped as they travel through splenic sinusoids. When these aged cells are broken down, their iron is recycled and the heme is converted to bilirubin, which the liver processes for excretion.

Although the liver also participates in processing red blood cell components (via Kupffer cells and bilirubin metabolism), the main destruction of senescent red blood cells happens in the spleen. The lungs and pancreas aren’t involved in breaking down aged red blood cells; the lungs handle gas exchange, and the pancreas functions in digestion and glucose regulation.