Spleen

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Spleen
Spleen
Laparoscopic view of a horse's spleen. (The purple and grey mottled organ).
Latin splen, lien
Gray's subject #278 1282
Artery Splenic artery
Vein Splenic vein
Nerve Splenic plexus
Precursor Mesenchyme of dorsal mesogastrium
MeSH Spleen
Dorlands/Elsevier s_19/12750780

The spleen is a ductless, vertebrate gland that is closely associated with the circulatory system, where it functions in the destruction of old red blood cells 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 is increasingly recognized that its absence leads to a predisposition to certain infections.

Contents

[edit] Anatomy

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 × 75 × 50 mm (5 × 3 × 2 in) in size, with an average weight of 150 g.

The spleen is the largest organ derived from mesenchyme and lying in the mesentery. The spleen 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 10% 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.

[edit] Embryology

The spleen appears during the fifth week of embryonic life as it develops from the mesenchyme of the dorsal mesogastrium. It begins dorsal to the stomach, but ends up on the stomach's left after the stomach undergoes its 90-degree rotation to the right, carrying dorsal structures to its left and anterior structures (eg, the liver) to its right.

[edit] Histology and functions

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:

Area Composition Function
red pulp Composed largely 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, especialy in the healthy adult:

  • Storage of red blood cells and other formed elements. This is more common in the adult than the creation of new red blood cells, but not as common as it is in some animals. 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.<ref name="MSNBC2006-Carey">Carey, Bjorn. "Horse science: What makes a Derby winner - Spleen acts as 'natural blood doper,' scientist says", MSNBC.com, Microsoft, May 5, 2006. Retrieved on 2006-05-09.</ref> 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.

[edit] Disorders

Enlargement of the spleen is known as splenomegaly. It may be caused by Sarcoidosis, malaria, bacterial endocarditis, leukaemia, pernicious anaemia, leishmaniasis, Hodgkin's disease, Banti's disease, hereditary spherocytosis, cysts, glandular fever (mononucleosis or 'Mono' caused by the Epstein-Barr Virus), and tumours. Primary tumours of the spleen include hemangiomas and hemangiosarcomas. Marked splenomegaly may result in the spleen occupying a large portion of the left side of the abdomen.

The spleen is the largest collection of lymphoid tissue in the body. It is normally palpable in preterm infants, in 30% of normal, full-term neonates, and in 5% to 10% of infants and toddlers. A spleen easily palpable below the costal margin in any child over the age of 3-4 years should be considered abnormal until proven otherwise.

Splenomegaly can result from antigenic stimulation (eg, infection), obstruction of blood flow (eg, portal vein obstruction), underlying functional abnormality (eg, hemolytic anemia), or infiltration (eg, leukemia or storage disease, such as Gaucher's disease). The most common cause of acute splenomegaly in children is viral infection, which is transient and usually moderate. Basic work-up for acute splenomegaly includes 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.

[edit] Absence

The absence of a spleen predisposes to some septicaemia infections. Vaccination and antibiotic measures are discussed under asplenia.

  • Some people congenitally completely lack a spleen, although this is rare.

[edit] Etymology and cultural views

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", (cognate with Old English milte). In 19th century England women in bad humour were said to be afflicted by spleen, or the vapours of spleen. In modern English "to vent one's spleen" means to vent one's anger, e.g. by shouting, and can be applied to both males and females.

In China, the spleen ' (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, although in the view of Traditional Chinese Medicine, the view of "脾" does not correspond to the anatomical "spleen".

[edit] See also

[edit] Additional images

[edit] Footnotes

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[edit] External links

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Lymphatic system
Bone marrow | Thymus (Hassall's corpuscles) | Spleen (White pulp, Periarteriolar lymphoid sheaths, Marginal zone, Red pulp) | Tonsils (Palatine, Lingual, Adenoid)

Mucosa-associated lymphoid tissue: Gut-associated lymphoid tissue | Peyer's patches

Lymph nodes: Cervical lymph nodes | Common iliac lymph nodes Deep inguinal lymph nodes | External iliac lymph nodes | Inferior mesenteric lymph nodes | Internal iliac lymph nodes | Lateral aortic lymph nodes | Paraaortic lymph node | Preaortic lymph nodes | Paratracheal chain | Retroaortic lymph nodes | Sentinel lymph node | Superficial inguinal lymph nodes | Virchow's node

Lymph vessels: Thoracic duct | Right lymphatic duct | Cisterna chyli  | Lumbar trunk | Intestinal trunk

Lymph | Lymphocytes | Immune system

da:Milt de:Milz es:Bazo eo:Lieno fr:Rate id:Limpa it:Milza he:טחול ka:ელენთა lt:Blužnis nl:Milt ja:脾臓 no:Milt nn:Milt pl:Śledziona pt:Baço ru:Селезёнка scn:Mèusa simple:Spleen sl:Vranica sr:Слезина su:Limpa fi:Perna sv:Mjälte th:ม้าม vi:Lách tr:Dalak zh:脾脏

Spleen

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