What is the average lifespan of a circulating erythrocyte in humans, and where are aged red cells predominantly removed?

• A 60 days, liver
• B 90 days, bone marrow
• C 120 days, spleen ✓
• D 180 days, lymph nodes

Explanation

Mature erythrocytes circulate for approximately 120 days before being phagocytosed by macrophages of the reticuloendothelial system, chiefly in the splenic red pulp. The spleen's narrow cords and slow transit expose senescent, less deformable cells to macrophages. The liver is the alternate site of destruction (important after splenectomy) but is secondary in the normal state. The other lifespans correspond to platelets (7 to 10 days) or granulocytes (hours to days), not erythrocytes.

Reference: Ganong Review of Medical Physiology, 26th ed.

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