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The spleen is an organ of vertebrates derived from mesenchyme[?] and lying in the mesentery[?]. It is closely associated with the circulatory system. The organ consists of masses of tissue of granular appearance, known as lymphoid tissue[?], located around fine terminal branches of veins and arteries. These vessels are connected through the spleen pulp by modified capillaries called splenic sinuses. The pulp is supported by a reticular tissue foundation and contains blood cells of all kinds in addition to the characteristic mesenchymal cells. The functions of the organ are the formation of blood cells, the destruction of old red blood corpuscles, the removal of other debris from the blood stream, and keeping a reservoir of blood.

The human spleen is located in the upper left part of the abdomen, behind the stomach and just below the diaphragm. In a normal individual this organ measures about 125 × 75 × 50 mm (5 × 3 × 2 in) in size. In certain diseases it often increases in size, and it may even fill a large portion of the left side of the abdomen. The spleen enlarges in malaria, bacterial endocarditis[?], leukemia, pernicious anemia[?], Hodgkins' disease[?], Banti's disease[?], and tumors, cysts of the spleen and glandular fever (mononucleosis).

The spleen is classified as a ductless gland and is also regarded as one of the centers of activity of the reticuloendothelial system[?]. Its presence is not necessary for life. It may be removed surgically, and often is following abdominal injuries with rupture and hemorrhage of the spleen, or in the treatment of certain blood diseases (hemorrhagic purpura[?], familial jaundice[?], etc.), or for the removal of splenic tumors or cysts. Congenital abnormalities such as accessory spleens occur, and rarely the spleen has been found to be completely absent. Sickle-cell disease can cause a functional asplenia by causing infarctions in the spleen during repeated sickle-cell crises.

In certain animals such as dogs and horses, the spleen sequesters a large number of erythrocytes (red blood cells), which can be dumped into the blood stream during periods of physical exertion. These animals also have large hearts in relation to their body size to accommodate the higher-viscosity blood that results. Some athletes have tried doping themselves with their own stored red cells to try to achieve the same effect, but the human heart is not equipped to handle the higher-viscosity blood.


The word spleen comes from the Greek splēn. In French, spleen refers to a state of pensive sadness or melancholy. It has been popularized by Baudelaire (XIX century) but was already used before, in particular in the Romantic literature (XVIII century). The connection between spleen (the organ) and melancholy (the temperament) comes from the humoral medicine of the ancient Greeks. One of the humours (body fluid) was the black bile, secreted by the spleen orgasm and associated with melancholy.

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