Spleen

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Spleen
Illu spleen.jpg
Spleen
Horse spleen laparoscopic.jpg
Laparoscopic view of a horse's spleen (the purple and grey mottled organ)
LatinLien
Greeksplḗn–σπλήν[1]
Gray'sp.1282
ArterySplenic artery
VeinSplenic vein
NerveSplenic plexus
PrecursorMesenchyme of dorsal mesogastrium
MeSHSpleen
Dorlands
/Elsevier
Spleen
Anatomical terminology
 
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For other uses, see Spleen (disambiguation).
Spleen
Illu spleen.jpg
Spleen
Horse spleen laparoscopic.jpg
Laparoscopic view of a horse's spleen (the purple and grey mottled organ)
LatinLien
Greeksplḗn–σπλήν[1]
Gray'sp.1282
ArterySplenic artery
VeinSplenic vein
NerveSplenic plexus
PrecursorMesenchyme of dorsal mesogastrium
MeSHSpleen
Dorlands
/Elsevier
Spleen
Anatomical terminology

The spleen (from Greek σπλήνsplḗn[2]) is an organ found in virtually all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter.

It is possible to remove the spleen without jeopardizing life. The spleen plays important roles in regard to red blood cells (also referred to as erythrocytes) and the immune system.[3] It removes old red blood cells and holds a reserve of blood, which can be valuable in case of hemorrhagic shock, and also recycles iron. As a part of the mononuclear phagocyte system, it metabolizes hemoglobin removed from senescent erythrocytes. The globin portion of hemoglobin is degraded to its constitutive amino acids, and the heme portion is metabolized to bilirubin, which is removed in the liver.[4]

The spleen synthesizes antibodies in its white pulp and removes antibody-coated bacteria and antibody-coated blood cells by way of blood and lymph node circulation. A study published in 2009 using mice found that the spleen contains, in its reserve, half of the body's monocytes within the red pulp.[5] These monocytes, upon moving to injured tissue (such as the heart), turn into dendritic cells and macrophages while promoting tissue healing.[5][6][7] The spleen is a center of activity of the mononuclear phagocyte system and can be considered analogous to a large lymph node, as its absence causes a predisposition to certain infections.[8]

In humans, the spleen is brownish in color and is located in the left upper quadrant of the abdomen.[4][9]

Structure[edit]

The spleen, in healthy adult humans, is approximately 7 centimetres (2.8 in) to 14 centimetres (5.5 in) in length. It usually weighs between 150 grams (5.3 oz)[10] and 200 grams (7.1 oz).[11] An easy way to remember the anatomy of the spleen is the 1×3×5×7×9×11 rule. The spleen is 1" by 3" by 5", weighs approximately 7 oz, and lies between the 9th and 11th ribs on the left hand side.

Surfaces[edit]

Visceral surface of the spleen

The diaphragmatic surface of the spleen (or phrenic surface) is convex, smooth, and is directed upward, backward, and to the left, except at its upper end, where it is directed slightly to the middle. It is in relation with the under surface of the diaphragm, which separates it from the ninth, tenth, and eleventh ribs of the left side, and the intervening lower border of the left lung and pleura.

The visceral surface of the spleen is divided by a ridge into two regions: an anterior or gastric and a posterior or renal. The gastric surface (facies gastrica) is directed forward, upward, and toward the middle, is broad and concave, and is in contact with the posterior wall of the stomach. Below this it is in contact with the tail of the pancreas. Near to its mid-border is a long fissure, termed the hilum. This is pierced by several irregular openings, for the entrance and exit of vessels and nerves. The renal surface (facies renalis) is directed medialward and downward. It is somewhat flattened, considerably narrower than the gastric surface, and is in relation with the upper part of the anterior surface of the left kidney and occasionally with the left suprarenal gland.

Like the thymus, the spleen possesses only efferent lymphatic vessels. The spleen is part of the lymphatic system. Both the short gastric arteries and the splenic artery supply it with blood.[12]

The germinal centers are supplied by arterioles called penicilliary radicles.[13]

Development[edit]

The spleen is unique in respect to its development within the gut. While most of the gut viscera are endodermally derived (with the exception of the neural-crest derived suprarenal gland), the spleen is derived from mesenchymal tissue.[14] Specifically, the spleen forms within, and from, the dorsal mesentery. However, it still shares the same blood supply—the celiac trunk—as the foregut organs.

Function[edit]

Micrograph of splenic tissue showing the red pulp (red), white pulp (blue) and a thickened inflamed capusule (mostly pink - top of image). H&E stain.
AreaFunctionComposition
red pulpMechanical filtration of red blood cells. In mice: Reserve of monocytes[5]
white pulpActive immune response through humoral and cell-mediated pathways.Composed of nodules, called Malpighian corpuscles. These are composed of:

Other functions of the spleen are less prominent, especially in the healthy adult:

Clinical significance[edit]

Main article: Splenic disease

Enlarged spleen[edit]

Main article: splenomegaly

Disorders include splenomegaly, where the spleen is enlarged for various reasons, such as cancer, specifically blood-based leukemias, and asplenia, where the spleen is not present or functions abnormally.

Traumas, such as a motor vehicle accident, can cause rupture of the spleen, which is a situation requiring immediate medical attention.

Decreased function[edit]

See also: Asplenia and Hyposplenia

Asplenia refers to a non-functioning spleen, which may be congenital or due to surgical removal. These may cause:[6]

A 28-year follow-up of 740 World War II veterans who had their spleens removed (splenectomy), on the battlefield, showed a significant increase in the usual death rate from pneumonia (6 rather than the expected 1.3) and an increase in the death rate from ischemic heart disease (4.1 rather than the expected 3) but not from other conditions.[20]

Society and culture[edit]

The word spleen comes from the Ancient Greek σπλήν (splḗn), and is the idiomatic equivalent of the heart in English, i.e. to be good-spleened (εὔσπλαγχνος, eúsplankhnos) means to be good-hearted or compassionate.[21]

In English the word spleen was customary during the period of the 18th century. Authors like Richard Blackmore or George Cheyne employed it to characterise the hypochondriacal and hysterical affections.[22][23] William Shakespeare, in Julius Caesar uses the spleen to describe Cassius' irritable nature.

Must I observe you? must I stand and crouch
Under your testy humour? By the gods
You shall digest the venom of your spleen,
Though it do split you; for, from this day forth,
I'll use you for my mirth, yea, for my laughter,
When you are waspish.[24]

In French, "splénétique" refers to a state of pensive sadness or melancholy. It has been popularized by the poet Charles Baudelaire (1821–1867) but was already used before in particular to the Romantic literature (19th century). The word for the organ is "rate".

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 while possibly suggesting a link with the humoral view of the organ. In eighteenth- and nineteenth-century England, women in bad humor were said to be afflicted by the spleen, or the vapours of the 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. Similarly, the English term "splenetic" is used to describe a person in a foul mood.

Other animals[edit]

In cartilaginous and ray-finned fish it consists primarily of red pulp and is normally a somewhat elongated organ as it actually lies inside the serosal lining of the intestine. In many amphibians, especially frogs, it takes on the more rounded form and there is often a greater quantity of white pulp.[25]

In reptiles, birds, and mammals, white pulp is always relatively plentiful, and in the latter two groups, the spleen is typically rounded, although it adjusts its shape somewhat to the arrangement of the surrounding organs. In the great majority of vertebrates, the spleen continues to produce red blood cells throughout life; it is only in mammals that this function is lost in adults. Many mammals have tiny spleen-like structures known as haemal nodes throughout the body that are presumed to have the same function as the spleen.[25] The spleens of aquatic mammals differ in some ways from those of fully land-dwelling mammals. In general, they are bluish in colour. In cetaceans and manatees they tend to be quite small, but in deep diving pinnipeds, they can be quite massive, due to their function of storing red blood cells.

The only vertebrates lacking a spleen are the lampreys and hagfishes. Even in these animals, there is a diffuse layer of haematopoeitic tissue within the gut wall, which has a similar structure to red pulp and is presumed to be homologous with the spleen of higher vertebrates.[25]

In mice, the spleen stores half the body's monocytes so that upon injury they can migrate to the injured tissue and transform into dendritic cells and macrophages and so assist wound healing.[5]

Gallery[edit]

See also[edit]

This article uses anatomical terminology; for an overview, see anatomical terminology.

References[edit]

  1. ^ σπλήν, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
  2. ^ σπλήν, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
  3. ^ Spleen, Internet Encyclopedia of Science
  4. ^ a b Mebius, RE; Kraal, G (2005). "Structure and function of the spleen". Nature reviews. Immunology 5 (8): 606–16. doi:10.1038/nri1669. PMID 16056254. 
  5. ^ a b c d Swirski, FK; Nahrendorf, M; Etzrodt, M; Wildgruber, M; Cortez-Retamozo, V; Panizzi, P; Figueiredo, JL; Kohler, RH; Chudnovskiy, A; Waterman, P; Aikawa, E; Mempel, TR; Libby, P; Weissleder, R; Pittet, MJ (2009). "Identification of splenic reservoir monocytes and their deployment to inflammatory sites". Science 325 (5940): 612–6. doi:10.1126/science.1175202. PMC 2803111. PMID 19644120. 
  6. ^ a b Jia, T; Pamer, EG (2009). "Immunology. Dispensable but not irrelevant". Science 325 (5940): 549–50. doi:10.1126/science.1178329. PMC 2917045. PMID 19644100. 
  7. ^ Finally, the Spleen Gets Some Respect By NATALIE ANGIER, The New York Times, August 3, 2009
  8. ^ Brender, MD, Erin; Allison Burke, MA, illustrator, Richard M. Glass, MD, editor (2005-11-23). "Spleen Patient Page" (PDF). Journal of the American Medical Association (American Medical Association) 294 (20): 2660. doi:10.1001/jama.294.20.2660. PMID 16304080. Retrieved 2008-03-20. 
  9. ^ Loscalzo, Joseph; Fauci, Anthony S.; Braunwald, Eugene; Dennis L. Kasper; Hauser, Stephen L; Longo, Dan L. (2008). Harrison's principles of internal medicine. McGraw-Hill Medical. ISBN 978-0-07-146633-2. 
  10. ^ eMedicine > Splenomegaly Author: David J Draper. Coauthor(s): Ronald A Sacher, Emmanuel N Dessypris, Lewis J Kaplan. Updated: Oct 4, 2009
  11. ^ Spielmann, Audrey L.; David M. DeLong; Mark A. Kliewer (1 January 2005). "Sonographic Evaluation of Spleen Size in Tall Healthy Athletes". American Journal of Roentgenology (American Roentgen Ray Society) 2005 (184): 45–49. doi:10.2214/ajr.184.1.01840045. PMID 15615949. Retrieved 2008-09-09. 
  12. ^ Blackbourne, Lorne H (2008-04-01). Surgical recall. Lippincott Williams & Wilkins. p. 259. ISBN 978-0-7817-7076-7. 
  13. ^ "Penicilliary radicles". Medical-dictionary.thefreedictionary.com. Retrieved 2011-04-03. 
  14. ^ Vellguth, Swantje; Brita von Gaudecker, Hans-Konrad Müller-Hermelink (1985). "The development of the human spleen". Cell and Tissue Research (Springer Berlin / Heidelberg) 242 (3): 579–592. doi:10.1007/BF00225424. 
  15. ^ Carey, Bjorn (May 5, 2006). "Horse science: What makes a Derby winner - Spleen acts as a 'natural blood doper,' scientist says". MSNBC.com. Retrieved 2006-05-09. 
  16. ^ "Spleen: Information, Surgery and Functions". Childrens Hospital of Pittsburgh - Chp.edu. 2010-11-17. Retrieved 2011-04-03. 
  17. ^ Di Sabatino, A; Carsetti, R; Corazza, GR (Jul 2, 2011). "Post-splenectomy and hyposplenic states". Lancet 378 (9785): 86–97. doi:10.1016/S0140-6736(10)61493-6. PMID 21474172. 
  18. ^ Carsetti, R; Rosado, MM; Wardmann, H (February 2004). "Peripheral development of B cells in mouse and man". Immunological reviews 197: 179–91. doi:10.1111/j.0105-2896.2004.0109.x. PMID 14962195. 
  19. ^ Kruetzmann, S; Rosado, MM; Weber, H; Germing, U; Tournilhac, O; Peter, HH; Berner, R; Peters, A; Boehm, T; Plebani, A; Quinti, I; Carsetti, R (Apr 7, 2003). "Human immunoglobulin M memory B cells controlling Streptococcus pneumoniae infections are generated in the spleen". The Journal of experimental medicine 197 (7): 939–45. doi:10.1084/jem.20022020. PMC 2193885. PMID 12682112. 
  20. ^ Dennis Robinette, C.; Fraumeni, Josephf. (1977). "Splenectomy and Subsequent Mortality in Veterans of the 1939-45 War". The Lancet 310 (8029): 127–9. doi:10.1016/S0140-6736(77)90132-5. PMID 69206. 
  21. ^ Robertson's Word Pictures of the New Testament, commentary on 1 Peter 3:8
  22. ^ Cheyne, George: The English Malady; or, A Treatise of Nervous Diseases of All Kinds, as Spleen, Vapours, Lowness of Spirits, Hypochondriacal and Hysterical Distempers with the Author's own Case at large, Dublin, 1733. Facsimile ed., ed. Eric T. Carlson, M.D., 1976, Scholars' Facsimiles & Reprints, ISBN 978-0-8201-1281-7;
  23. ^ Blackmore, Richard: Treatise of the spleen and vapors. London, 1725
  24. ^ Julius Caesar by William Shakespeare Act 4:1
  25. ^ a b c Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia: Holt-Saunders International. pp. 410–411. ISBN 0-03-910284-X. 

External links[edit]