|Laparoscopic view of a horse's spleen. (The purple and gray mottled organ).|
|Gray's||subject #278 1282|
|Precursor||Mesenchyme of dorsal mesogastrium|
The spleen is a vascular lymphoid organ found in most vertebrates, normally close to the stomach in the abdominal cavity, and that functions in various activities related to the circulatory system and the immune system. The spleen is involved in filtering blood of foreign invaders and old red blood cells (erythrocytes), destruction of old red blood cells and recycling hemoglobin, storing blood and holding a reservoir of red blood cells, producing lymphocytes, sometimes serving as a center for forming red blood cells, and possibly forming antibodies. It is regarded as one of the centers of activity of the reticuloendothelial system (part of the immune system).
As with other parts of the body (cells, tissues, other organs, and organ systems), the spleen provides larger benefit to the body and likewise is dependent on other organs, as well as cells, tissues, and organ systems, for its own proper functioning. This principle whereby each body part provides some benefit to the whole and to other body parts, while also receiving benefit, underlies the complex coordination and harmony seen in organisms.
Until recently, the purpose of the spleen was not known. Historically, it was considered the seat of passion or emotion, and thus its expression in the modern English phrase "vent one's spleen."
It is increasingly recognized that its absence leads to a predisposition to certain infections.
The human spleen is located in the upper left part of the abdomen, behind the stomach and just below the diaphragm. In normal individuals, this organ measures about 125 by 75 by 50 millimeters (5 by 3 by 2 inches) in size, with an average weight of 150 grams.
The spleen is the largest organ derived from mesenchyme and lying in the mesentery. It consists of masses of lymphoid tissue of granular appearance located around fine terminal branches of veins and arteries. These vessels are connected by modified capillaries called splenic sinuses.
Approximately ten persent of people have one or more accessory spleens. They may form near the hilum of the main spleen, the junction at which the splenic vessels enter and leave the organ.
There are several peritoneal ligaments that support the spleen:
To understand this terminology, it helps to know that "lien" is an alternate root for "spleen."
Cross sections of the spleen reveal a red soft surface, which is divided into two types of pulp which correspond to the two most important functional roles of the spleen, summarized below:
|Red pulp||Composed of:
* "sinuses" (or "sinusoids"), which are filled with blood
* "splenic cords" of reticular fibers
* "marginal zone" bordering on white pulp
|Mechanical filtration. Removes unwanted materials from the blood, including senescent red blood cells.|
|White pulp||Composed of nodules, called Malpighian corpuscles. These are composed of:
* "lymphoid follicles" (or "follicles"), rich in B-lymphocytes
* "periarteriolar lymphoid sheaths" (PALS), rich in T-lymphocytes
|Helps fight infections.|
Other functions of the spleen are less prominent, especially in the healthy adult:
In certain mammals, not humans, there is another function of the spleen:
Enlargement of the spleen is known as splenomegaly. It may be caused by malaria, sarcoidosis, infectious mononucleosis, bacterial endocarditis, leukemia, pernicious anemia, Gaucher's disease, leishmaniasis, or Hodgkin's disease]]. Splenomegaly diagnosis involves a complete blood count with differential, platelet count, and reticulocyte and atypical lymphocyte counts to exclude hemolytic anemia and leukemia. Assessment of IgM antibodies to viral capsid antigen (a rising titer) is indicated to confirm Epstein-Barr virus or cytomegalovirus. Other infections should be excluded if these tests are negative.
The absence of a spleen predisposes to some septicemia infections.
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 (eighteenth century). The connection between spleen (the organ) and melancholy (the temperament) comes from the humoral medicine of the ancient Greeks. One of the humors (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," (cognate with Old English milte). In nineteenth-century England, women in bad humor were said to be afflicted by spleen, or the vapors of spleen. In modern English "to vent one's spleen" means to vent one's anger, such as by shouting, and can be applied to both males and females.
In China, the spleen 脾 (pí) counts as the seat of one's temperament and is thought to influence the individual's willpower. Analogous to "venting one's spleen," 发脾气 is used as an expression for getting angry, although in the view of traditional Chinese medicine, the view of "脾" does not correspond to the anatomical "spleen."
|Lymphatic system - edit|
|Lymph nodes | Lymph | Lymphocytes | Lymph vessels | Thoracic duct | Immune system | Bone marrow | Spleen | Thymus | Tonsils|
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