The spleen is a hematopoietic organ capable of supporting elements of the erythroid, myeloid, megakaryocytic, lymphoid, and monocyte-macrophage (ie, reticuloendothelial) systems . As such, it is important in the following situations:
●The spleen participates in cellular and humoral immunity through its lymphoid elements. (See "The adaptive cellular immune response" and "The humoral immune response".)
●The spleen is involved with the removal of senescent red blood cells, bacteria, and other particulates from the circulation through elements of the monocyte-macrophage system. An increase in this function (ie, hypersplenism) may be associated with varying degrees of cytopenia, while removal of the spleen (ie, asplenia) may render the patient susceptible to bacterial sepsis, especially with encapsulated organisms . (See "Extrinsic nonimmune hemolytic anemia due to mechanical damage: Fragmentation hemolysis and hypersplenism", section on 'Extravascular nonimmune hemolysis due to hypersplenism' and "Clinical features and management of sepsis in the asplenic patient" and "Prevention of sepsis in the asplenic patient".)
●Splenectomy in patients with various hematologic disorders (eg, polycythemia vera, essential thrombocythemia, thalassemia, stomatocytosis) has been associated with an increased incidence of vascular complications, including venous and arterial thrombosis and pulmonary hypertension [2,3].
●Normally, about one-third of circulating platelets are sequestered in the spleen, where they are in equilibrium with circulating platelets. (See "Approach to the adult patient with thrombocytopenia", section on 'Dilutional thrombocytopenia' and "Approach to the adult patient with thrombocytopenia", section on 'Distributional thrombocytopenia caused by splenomegaly'.)