Normal red blood cells (RBCs) have no nuclei, and as such, have a limited capacity to maintain cellular integrity.  After about 120 days in circulation, RBCs are removed by macrophages in the reticulo-endothelial system (mainly marrow). The normal red cell cycle is shown below.

Normal Red Cell Cycle. Steps 1 and 2 are covered in the section on erythropoiesis. 3. After phagocytosis by macrophages in the reticuloendothelial system, haemoglobin is broken down into globin (4) and heme (5). Heme in turn is broken down into bilirubin and iron, which binds to transferrin and is recycled. 6. The breakdown products are taken up by the liver – bilirubin is used to make bile, while iron is stored in ferritin. Image credit: OpenStax College (CC BY 3.0)