How does the spleen remove old red blood cells from circulation?

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Diagram of the human lymphatic system highlighting lymphatic vessels and major lymphoid organs, including lymph nodes, adenoids, tonsils, thymus gland, spleen, appendix, bone marrow, and ducts. — lymphatic system The human lymphatic system, showing the lymphatic vessels and lymphoid organs.

The spleen, an organ of the lymphatic system, functions as the primary filter for the blood. Within the spleen, the red pulp is the specific site where the body destroys old or degenerate red blood cells, which typically have a lifespan of about 120 days.1

This process occurs as blood passes through the red pulp, which consists of a network of splenic cords and sinusoids. Macrophages—specialized phagocytic cells—reside in the red pulp and are responsible for removing these aging cells from circulation. Once the red blood cells are captured, the hemoglobin they contain is broken down into an excretable pigment and an iron molecule, the latter of which is recycled by the body to produce new hemoglobin.1