hematology and oncology
Overview of the Spleen
Introduction
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. is a site of production and maturation of B cells and removes antibody-coated bacteria, senescent or defective red blood cells (RBCs), and antibody-coated blood cells (as may occur in immune cytopenias such as Immune Thrombocytopenia (ITP) , In some animals, the spleen can contract at times of severe anemia and "autotransfuse" red cells; whether this "autotransfusion" occurs in humans is unclear. Using its culling and pitting functions for RBCs, the spleen removes inclusion bodies, such as Heinz bodies (precipitates of insoluble globin), Howell-Jolly bodies (nuclear DNA 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 or if stimulated by therapy with hematopoietic growth factors (see also Primary Myelofibrosis (PMF) and -related neurons in some areas of the brain. Splenectomy or splenic denervation has been shown to prevent stress-related depression in laboratory animals ( General reference ). 