Overview of the spleen

[Marquetta]

The spleen, a spongy, soft organ about as big as a person’s fist, is located in the upper left part of the abdomen, just under the rib cage. The splenic artery brings blood to the spleen from the heart. Blood leaves the spleen through the splenic vein, which drains into a larger vein (the portal vein) that carries the blood to the liver. The spleen has a covering of fibrous tissue (the splenic capsule) that supports its blood vessels and lymphatic vessels.
The spleen is made up of two basic types of tissue, each with different functions:

White pulp
Red pulp

The white pulp is part of the infection-fighting system (immune system). It produces white blood cells called lymphocytes, which in turn produce antibodies (specialized proteins that protect against invasion by foreign substances).
The red pulp filters the blood, removing unwanted material. The red pulp contains other white blood cells called phagocytes that ingest microorganisms, such as bacteria, fungi, and viruses. It also monitors red blood cells, destroying those that are abnormal or too old or damaged to function properly. In addition, the red pulp serves as a reservoir for different elements of the blood, especially white blood cells and platelets (cell-like particles involved in clotting). However, releasing these elements is a minor function of the red pulp.

[Hina Muqadas]

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 white pulp is a site of production and maturation of B cells and T cells. B cells in the spleen generate protective humoral antibodies; in certain autoimmune disorders (eg, immune thrombocytopenia [ITP], Coombs-positive immune hemolytic anemias), inappropriate autoantibodies to circulating blood elements also may be synthesized.
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, Coombs-positive hemolytic anemias, and some neutropenias). The red pulp also serves as a reservoir for blood elements, especially white blood cells (WBCs) and platelets.
In some animals, the spleen can contract at times of severe anemia and quot;autotransfusequot; red cells; whether this quot;autotransfusionquot; 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 repopulate the adult spleen (see also Primary Myelofibrosis and Myelodysplastic Syndrome).