Final answer:
Red blood cells, or erythrocytes, have an average lifespan of 120 days in the circulation before being removed by macrophages in the liver and spleen.
Step-by-step explanation:
Red blood cells, also known as erythrocytes, have an average lifespan of 120 days in the circulation. After this time, they are removed by macrophages, a type of white blood cell, primarily in the liver and spleen. The components of the degraded red blood cells' hemoglobin are then further processed.