For other uses, see API (disambiguation).

spleen
Spleen
Laparoscopic view of a horse's spleen (the purple and grey mottled organ)
Latin | Lien (Greek: Splen)
Gray's | subject #278 1282
Artery | Splenic artery
Vein | Splenic vein
Nerve | Splenic plexus
Precursor | Mesenchyme of dorsal mesogastrium
MeSH | Spleen
Dorlands/Elsevier | Spleen

The spleen (from Greek ??????spl?n[1]) is an organ found in virtually all vertebrate animals. Similar in structure to a large lymph node, the spleen acts primarily as a blood filter. As such, it is a non-vital organ, with life possible after removal. The spleen plays important roles in regard to red blood cells (also referred to as erythrocytes) and the immune system.[2] In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock while also recycling 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 subsequently shuttled to the liver for removal.[3] It synthesizes antibodies in its white pulp and removes antibody-coated bacteria along with antibody-coated blood cells by way of blood and lymph node circulation. The spleen is brownish in color.[3][4] A study published in 2009 using mice showed it has been found to contain 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] It is one of the centers of activity of the reticuloendothelial system and can be considered analogous to a large lymph node, as its absence leads to a predisposition toward certain infections.[8]

## Anatomy[edit]

The spleen, in healthy adult humans, is approximately 11 centimetres (4.3 in) in length. It usually weighs between 150 grams (5.3 oz)[9] and 200 grams (7.1 oz).[10] 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.

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.[11]

The germinal centers are supplied by arterioles called penicilliary radicles.[12]

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.[13] 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). HE stain.

Area | Function | Composition
red pulp | Mechanical filtration of red blood cells. In mice: Reserve of monocytes[5] | "sinuses" (or "sinusoids"), which are filled with blood "splenic cords" of reticular fibers "marginal zone" bordering on white pulp
white pulp | Active immune response through humoral and cell-mediated pathways. | 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

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

- Production of opsonins, properdin, and tuftsin.
- Creation of red blood cells. While the bone marrow is the primary site of hematopoiesis in the adult, the spleen has important hematopoietic functions up until the fifth month of gestation. After birth, erythropoietic functions cease, except in some hematologic disorders. As a major lymphoid organ and a central player in the reticuloendothelial system, the spleen retains the ability to produce lymphocytes and, as such, remains an hematopoietic organ.
- Storage of red blood cells, lymphocytes and other formed elements. In horses, roughly 30% of the red blood cells are stored there. The red blood cells can be released when needed.[14] In humans, up to a cup (236.5 ml) of red blood cells can be held in the spleen and released in cases of hypovolemia.[15] It can store platelets in case of an emergency. Up to a quarter of lymphocytes can be stored in the spleen at any one time.
- 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]

## Effects of removal[edit]

See also: Asplenia

Surgical removal causes:[6]

- modest increases in circulating white blood cells and platelets,
- diminished responsiveness to some vaccines,
- increased susceptibility to infection by bacteria and protozoa; in particular, there is an increased risk of sepsis from polysaccharide encapsulated bacteria.

A 28-year follow-up of 740 veterans of World War II who had their spleens removed on the battlefield found that those who had been splenectomized showed a significant excess of mortality from pneumonia (6 rather than the expected 1.3) and a significant excess of mortality from ischemic heart disease (4.1 rather than the expected 3) but not from other conditions.[16]

## Disorders[edit]

Main article: Splenic disease

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.

## Etymology and cultural views[edit]

The word spleen comes from the Greek ????? (spl?n), and is the idiomatic equivalent of the heart in English, i.e. to be good-spleened (???????????, e?splankhnos) means to be good-hearted or compassionate.[17]

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.[18][19] 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.[20]

In French, "spl?n?tique" 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 "la 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 the eighteenth- and nineteenth-century England, women in bad humour 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.

## Variation among vertebrates[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.[21]

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 the adult. Many mammals possess tiny spleen-like structures known as haemal nodes throughout the body, which, it is presumed, have the same function as the spleen proper.[21] The spleens of aquatic mammals are in some ways dissimilar to those of fully land-dwelling mammals. In general, the spleens of aquatic mammals are bluish in colour. In cetaceans and manatees it tends to be quite small, but in deep diving pinnipeds it can be quite massive, owing to its 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.[21]

## See also[edit]

- Marginal zone

## Gallery[edit]

- The celiac artery and its branches.

- The celiac artery and its branches.

- Horizontal disposition of the peritoneum in the upper part of the abdomen.

- Transverse section through the middle of the first lumbar vertebra.

- The duodenum and pancreas.

- The visceral surface of the spleen.

- Transverse section of the spleen, showing the trabecular tissue and the splenic vein and its tributaries.

- Transverse section of the human spleen, showing the distribution of the splenic artery and its branches.

- Section of the spleen, showing the termination of the small blood vessels.

- Back of lumbar region, showing surface markings for kidneys, ureters, and spleen.

- Side of thorax, showing surface markings for bones, lungs (purple), pleura (blue), and spleen (green).

- Lymphatic system

- Spleen

- Spleen (lien)

- Spleen

## References[edit]

1. ^ ?????, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
2. ^ Spleen, Internet Encyclopedia of Science
3. ^ a b Mebius RE, Kraal G. (2005). Structure and function of the spleen. Nat Rev Immunol. 5(8):606?16. PMID 16056254
4. ^ 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.
5. ^ a b c d Swirski FK, Nahrendorf M, Etzrodt M, Wildgruber M, Cortez-Retamozo V, Panizzi P, Figueiredo J-L, 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: 612?616. doi:10.1126/science.1175202 Swirski, F. K.; Nahrendorf, M.; Etzrodt, M.; Wildgruber, M.; Cortez-Retamozo, V.; Panizzi, P.; Figueiredo, J. -L.; Kohler, R. H.; Chudnovskiy, A.; Waterman, P.; Aikawa, E.; Mempel, T. R.; Libby, P.; Weissleder, R.; Pittet, M. J. (2009). "Identification of Splenic Reservoir Monocytes and Their Deployment to Inflammatory Sites". Science 325 (5940): 612–616. doi:10.1126/science.1175202. PMC 2803111. PMID 19644120. edit
6. ^ a b Jia T, Pamer EG. (2009). Dispensable But Not Irrelevant. Science, 325:549?550. doi:10.1126/science.1178329 Jia, T.; Pamer, E. G. (2009). "Dispensable but Not Irrelevant". Science 325 (5940): 549–550. doi:10.1126/science.1178329. PMC 2917045. PMID 19644100. edit
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. More than one of `|author=` and `|last=` specified (help)
9. ^ eMedicine > Splenomegaly Author: David J Draper. Coauthor(s): Ronald A Sacher, Emmanuel N Dessypris, Lewis J Kaplan. Updated: Oct 4, 2009
10. ^ 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. PMID 15615949. Retrieved 2008-09-09.
11. ^ Blackbourne, Lorne H (2008-04-01). Surgical recall. Lippincott Williams Wilkins. p. 259. ISBN 978-0-7817-7076-7.
12. ^ radicles "Penicilliary radicles". Medical-dictionary.thefreedictionary.com. Retrieved 2011-04-03.
13. ^ Vellguth, Swantje; Brita von Gaudecker, Hans-Konrad M?ller-Hermelink. "The development of the human spleen". Cell and Tissue Research (Springer Berlin / Heidelberg) 242 (3): 579?592. Retrieved 2009-02-14.
14. ^ 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.
15. ^ spleen functions "Spleen: Information, Surgery and Functions". Childrens Hospital of Pittsburgh - Chp.edu. 2010-11-17. Retrieved 2011-04-03.
16. ^ Robinette CD, Fraumeni JF Jr. (1977). Splenectomy and subsequent mortality in veterans of the 1939?45 war. Lancet. Jul 16;2(8029):127?9. PubMed doi:10.1016/S0140-6736(77)90132-5
17. ^ Robertson's Word Pictures of the New Testament, commentary on 1 Peter 3:8
18. ^ 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;
19. ^ Blackmore, Richard: Treatise of the spleen and vapors. London, 1725
20. ^ Julius Caesar by William Shakespeare Act 4:1
21. ^ 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]

| Look up spleen in Wiktionary, the free dictionary.

| Wikimedia Commons has media related to Spleen.

- SUNY Figs 38:03-01?"The visceral surface of the spleen."
- SUNY Anatomy Image 7881
- "spleen" from Encyclop?dia Britannica Online
- Spleen and Lymphatic System, Kidshealth.org (American Academy of Family Physicians)
- Spleen Diseases from MedlinePlus
- "Finally, the Spleen Gets Some Respect" New York Times piece on the spleen

Systems and organs of the animal anatomy
Respiratory system | Bronchus Trachea Lung Diaphragm
Excretory system | Kidney Bladder
Nervous system | Brain
Immune system | Spleen Adenoid
Digestive system | Anus Colon Mouth Pancreas Rectum Small intestine Spleen Stomach Tongue Tooth Vermiform appendix
Other organs | Bone Ear Eye Head Heart Larynx Liver Nose Penis Pharynx Rhinarium Skeleton Skin Skull Tonsil Thymus Thyroid
Tissues | Tissue (biology)

Lymphoid system (TA A13.1–2, TH H3.10, GA 8 and 9)
Primary lymphoid organs |
Bone marrow | Hematopoietic stem cell
Thymus | Cortex Medulla Hassall's corpuscles
Secondary lymphoid organs |
Spleen (process blood) | structural: Hilum Trabeculae Diaphragmatic surface of spleen Visceral surface of spleen Red pulp Cords of Billroth Marginal zone White pulp Periarteriolar lymphoid sheaths Germinal center blood flow: Trabecular arteries Trabecular veins
Tonsils/Waldeyer's tonsillar ring | Palatine Lingual Pharyngeal Tubal Tonsillar crypts
Lymph nodes (process extracellular fluid) | lymph flow: Afferent lymph vessels Cortical sinuses Medullary sinuses Efferent lymph vessels T cells: High endothelial venules B cells: Primary follicle/Germinal center Mantle zone Marginal zone layers: Capsule/Trabeculae Subcapsular sinus Cortex Paracortex Medulla (Medullary cord) Hilum
MALT (process mucosa) | GALT Peyer's patch Germinal center
M: LMO | anat (h, u, t, a, l)/phys/devp | noco/cong/tumr | proc