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Overview of the Spleen

By

Harry S. Jacob

, MD, DHC, University of Minnesota Medical School

Last full review/revision Apr 2021| Content last modified Apr 2021
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By structure and function, the spleen is essentially 2 organs:

  • The white pulp, consisting of periarterial lymphatic sheaths and germinal centers, acts as an immune organ.

  • The red pulp, consisting of macrophages and granulocytes lining vascular spaces (the cords and sinusoids), acts as a phagocytic organ.

The red pulp removes antibody-coated bacteria, senescent or defective red blood cells (RBCs), and antibody-coated blood cells (as may occur in immune cytopenias such as ITP Immune Thrombocytopenia (ITP) Immune thrombocytopenia (ITP) is a bleeding disorder usually without anemia or leukopenia. Typically, it is chronic in adults, but it is usually acute and self-limited in children. Spleen size... read more Immune Thrombocytopenia (ITP) , Coombs-positive hemolytic anemias Autoimmune Hemolytic Anemia Autoimmune hemolytic anemia is caused by autoantibodies that react with red blood cells at temperatures ≥ 37° C (warm antibody hemolytic anemia) or 37° C (cold agglutinin disease). Hemolysis... read more Autoimmune Hemolytic Anemia , and some neutropenias Neutropenia Neutropenia is a reduction in the blood neutrophil count. If it is severe, the risk and severity of bacterial and fungal infections increase. Focal symptoms of infection may be muted, but fever... read more ). The red pulp also serves as a reservoir for blood elements, especially white blood cells (WBCs) and platelets. Macrophages derived from blood monocytes and resident macrophages produced during embryonic development and resident can be activated to amplify control of infection, but they can produce substances that induce unwanted excessive inflammation (eg, in the brain after cerebral infarction).

In some animals, the spleen can contract at times of severe anemia and "autotransfuse" red cells; whether this "autotransfusion" occurs in humans is unclear. During its culling and pitting of RBCs, the spleen removes inclusion bodies, such as Heinz bodies (precipitates of insoluble globin), Howell-Jolly bodies (nuclear remnants), whole nuclei, and malformed RBCs; thus, after splenectomy or in the functionally hyposplenic state, RBCs with these inclusions and acanthocytes (a type of malformed RBC) appear in the peripheral circulation. Extramedullary hematopoiesis may occur if injury to bone marrow (eg, by fibrosis or tumor metastases) allows hematopoietic stem cells to circulate and populate the adult spleen (see also Primary Myelofibrosis Primary Myelofibrosis Primary myelofibrosis (PMF) is a chronic myeloproliferative neoplasm characterized by bone marrow fibrosis, splenomegaly, and anemia with nucleated and teardrop-shaped red blood cells. Diagnosis... read more and Myelodysplastic Syndrome Myelodysplastic Syndrome (MDS) The myelodysplastic syndrome (MDS) is group of disorders typified by peripheral cytopenia, dysplastic hematopoietic progenitors, a hypercellular or hypocellular bone marrow, and a high risk... read more ).

Asplenia

Asplenia is loss of splenic function due to

  • Congenital absence of the spleen

  • Functional absence of the spleen

  • Surgical removal of the spleen (splenectomy)

Because of the risk of these infections, immunization is important. Patients should receive the pneumococcal vaccine Pneumococcal Vaccine Pneumococcal disease (eg, otitis media, pneumonia, sepsis, meningitis) is caused by some of the > 90 serotypes of Streptococcus pneumoniae (pneumococci). Vaccines are directed against many of... read more , the meningococcal vaccine Meningococcal Vaccine The meningococcal serogroups that most often cause meningococcal disease in the US are serogroups B, C, and Y. Serogroups A and W cause disease outside the US. Current vaccines are directed... read more , and the Haemophilus influenzae b vaccine Haemophilus influenzae Type b (Hib) Vaccine Haemophilus influenzae type b (Hib) vaccines help prevent Haemophilus infections but not infections caused by other strains of H. influenzae bacteria. H. influenzae causes many childhood infections... read more . Patients should also receive the influenza vaccine Influenza Vaccine Based on recommendations by the World Health Organization and the Centers for Disease Control and Prevention (CDC), vaccines for influenza are modified annually to include the most prevalent... read more and other vaccinations according to their clinical situation. Patients also are often given daily prophylactic antibiotics such as penicillin or amoxicillin, particularly when they have regular contact with children. The appropriate duration for prophylactic antibiotic use is unclear. Patients with asplenia who develop fever should receive empiric antibiotics while undergoing evaluation for the source.

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