Spleen

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 lymphoid tissue of granular appearance located around fine terminal branches of veins and arteries. These vessels are connected through the splenic pulp by modified capillaries called splenic sinuses. Cross sections of the spleen reveal a red soft surface which is divided into red and white pulp. Red pulp corresponds to the sinuses which are usually filled with blood. The white pulp shows white nodules, called Malpighian corpuscles. Under the microscope, these areas correspond to lymphoid follicles, rich in B-lymphocytes, and the periarteriolar lymphoid sheaths, rich in T-lymphocytes. The functions of the organ are the destruction of old red blood cell, the removal of other debris from the bloodstream, 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, leukaemia, pernicious anaemia, Hodgkin's disease, Banti's disease, and tumours, cysts of the spleen and glandular fever (mononucleosis).

The spleen is classified as a ductless gland and is also regarded as one of the centres of activity of the reticuloendothelial system. Until recently, the purpose of the spleen was not known. Its presence is not necessary for life. It may be removed surgically, and often is following abdominal injuries with rupture and haemorrhage of the spleen, or in the treatment of certain blood diseases (haemorrhagic purpura, familial jaundice, etc.), or for the removal of splenic tumours 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 bloodstream 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 blood cells to try to achieve the same effect, but the human heart is not equipped to handle the higher-viscosity blood.

Origin

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 the poet Charles-Pierre Baudelaire (1821-1867) but was already used before, in particular in the Romantic literature (18th 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 organ and associated with melancholy.

In German, spleen refers to a persisting somewhat cranky (but not quite lunatic) idea or habit of a person.

Intestingly, the Talmud (tractate Berachoth 61b) refers to the spleen as the organ of laughter, possibly suggesting a link with the humoral view of the organ.