What is the function of the human spleen?
The human spleen performs the following functions:
1. Hematopoietic function: During embryonic development, the spleen serves as a major hematopoietic organ. In adults, although hematopoiesis primarily occurs in the bone marrow, the spleen retains a small number of hematopoietic stem cells. Under conditions of severe anemia or certain disease states, the spleen can resume production of red blood cells, platelets, and other blood components to meet the body’s demands.

2. Blood reservoir function: The spleen acts as an important reservoir for blood. During emergencies—such as acute massive hemorrhage—the spleen contracts, releasing stored blood cells into systemic circulation to supply vital organs, thereby serving both as a blood reserve and as a compensatory mechanism against hypovolemic shock.
3. Filtration function: The spleen is an efficient blood filter. As blood passes through the spleen, bacteria and senescent or damaged blood cells are phagocytosed and digested by abundant macrophages residing within the splenic tissue.

4. Immune function: The spleen is the largest peripheral lymphoid organ in the human body and produces immunoglobulins and other immune mediators, playing a critical role in immune defense. However, with advancing age, the spleen’s immune function gradually declines.