Spleen
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The spleen is a ductless, vertebrate gland that is not necessary for life but is closely associated with the circulatory system, where it functions in the destruction of old red blood cells and removal of other debris from the bloodstream, and also in holding a reservoir of blood. It is regarded as one of the centres of activity of the reticuloendothelial system. Until recently, the purpose of the spleen was not known. It may be removed surgically (known as a splenectomy), and indeed often is. The spleen is often removed, for example, following abdominal injuries with rupture and haemorrhage of the spleen, or in the treatment of certain blood diseases (haemorrhagic purpura, familial jaundice, hereditary spherocytosis, etc.), or for the removal of splenic tumours or cysts.
It is an organ derived from mesenchyme and lying in the mesentery. 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 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. Enlargement of the spleen, also known as splenomegaly, occurs in many diseases and disorders, including malaria, bacterial endocarditis, leukaemia, pernicious anaemia, Hodgkin's disease, Banti's disease, tumours and cysts of the spleen, glandular fever (mononucleosis), and hereditary spherocytosis.
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 contrast, 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.
In German, the word "spleen", pronounced as in English, refers to a persisting somewhat cranky (but not quite lunatic) idea or habit of a person; however the organ is called "Milz". In 19th century England women in bad humour were said to be afflicted by spleen, or the vapours of spleen.
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Lymph nodes - Lymph - Lymphocytes - Lymph vessels - Thoracic duct |
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Bone marrow - Spleen - Thymus - Tonsils |