In humans, the spleen is underneath the left part of thediaphragm, and has a smooth, convex surface that faces the diaphragm. It is underneath the ninth, tenth, and eleventh ribs. The other side of the spleen is divided by a ridge into two regions: an anterior gastric portion, and a posteriorrenal portion. The gastric surface is directed forward, upward, and toward the middle, is broad and concave, and is in contact with the posterior wall of thestomach. Below this it is in contact with the tail of thepancreas. The renal surface 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 leftadrenal gland.
The spleen, in healthy adult humans, is approximately 7 to 14 centimetres (3 to5+1⁄2 in) in length.
An easy way to remember the anatomy of the spleen is the 1×3×5×7×9×10×11 rule. The spleen is 1 by 3 by 5 inches (3 by 8 by 13 cm), weighs approximately 7 oz (200 g), and lies between the ninth and eleventh ribs on the left-hand side and along the axis of the tenth rib. The weight varies between 1 oz (28 g) and 8 oz (230 g) (standardreference range),[12] correlating mainly to height, body weight and degree of acute congestion but not to sex or age.[13]
Near the middle of the spleen is a long fissure, thehilum, which is the point of attachment for thegastrosplenic ligament and the point of insertion for thesplenic artery andsplenic vein. There are other openings present forlymphatic vessels andnerves. In addition to the splenic artery, collateral blood supply is provided by the adjacent short gastric arteries.[14]
The spleen is unique in respect to its development within thegut. While most of the gutorgans areendodermally derived, the spleen is derived frommesenchymal tissue.[18] Specifically, the spleen forms within, and from, thedorsal mesentery. However, it still shares the same blood supply—theceliac trunk—as theforegut organs.
Micrograph of splenic tissue showing the red pulp (red), white pulp (blue nuclei in lighter background) and athickened inflamed capsule (mostly pink – top of image).H&E stain.The spleen contains two different tissues, white pulp (A) and red pulp (B). The white pulp functions in producing and growing immune and blood cells. The red pulp functions in filtering blood of antigens, microorganisms, and defective or worn-out red blood cells.
Creation ofred blood cells. While thebone marrow is the primary site ofhematopoiesis 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 thereticuloendothelial system, the spleen retains the ability to produce lymphocytes and, as such, remains a hematopoietic organ.
Storage ofred blood cells,lymphocytes and other formed elements. The spleen of horses stores roughly 30 percent of the red blood cells and can release them when needed.[20] In humans, up to a cup (240 ml) of red blood cells is held within the spleen and released in cases ofhypovolemia[21] andhypoxia.[22] It can storeplatelets in case of an emergency and also clears old platelets from the circulation. Up to a quarter oflymphocytes are stored in the spleen at any one time.
The spleen is the largest collection oflymphoid tissue in the body. It is normally palpable in preterm infants, in 30% of normal, full-termneonates, and in 5% to 10% of infants and toddlers. A spleen easily palpable below thecostal margin in any child over the age of three to four years should be considered abnormal until proven otherwise.
Splenomegaly can result from antigenic stimulation (e.g., infection), obstruction of blood flow (e.g., portal vein obstruction), underlying functional abnormality (e.g.,hemolytic anemia), or infiltration (e.g.,leukemia or storage disease, such asGaucher'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 acomplete blood count with differential, platelet count, andreticulocyte and atypical lymphocyte counts to exclude hemolytic anemia and leukemia. Assessment ofIgM antibodies to viral capsid antigen (a risingtiter) is indicated to confirm Epstein–Barr virus orcytomegalovirus. Other infections should be excluded if these tests are negative.
Calculators have been developed for measurements of spleen size based onCT,US, andMRI findings.
Asplenia refers to a non-functioning spleen, which may becongenital, or caused by traumatic injury, surgical resection (splenectomy) or a disease such assickle cell anaemia. Hyposplenia refers to a partially functioning spleen. These conditions may cause[6] a modest increase in circulatingwhite blood cells andplatelets, a diminished response to somevaccines, and an increased susceptibility to infection. In particular, there is an increased risk ofsepsis frompolysaccharide encapsulated bacteria. Encapsulated bacteria inhibit binding of complement or prevent complement assembled on the capsule from interacting with macrophage receptors. Phagocytosis needs natural antibodies, which are immunoglobulins that facilitate phagocytosis either directly or by complement deposition on the capsule. They are produced byIgMmemory B cells (a subtype ofB cells) in themarginal zone of the spleen.[23][24]
Asplenectomy (removal of the spleen) results in a greatly diminished frequency of memory B cells.[25] A 28-year follow-up of 740World War II veterans whose spleens were removed on the battlefield showed a significant increase in the usual death rate frompneumonia (6 rather than the expected 1.3) and an increase in the death rate fromischemic heart disease (41 rather than the expected 30), but not from other conditions.[26]
Anaccessory spleen is a small splenic nodule extra to the spleen usually formed in earlyembryogenesis. Accessory spleens are found in approximately 10 percent of the population[27] and are typically around 1 centimeter in diameter.Splenosis is a condition where displaced pieces of splenic tissue (often followingtrauma or splenectomy)autotransplant in the abdominal cavity as accessory spleens.[28]
Polysplenia is a congenital disease manifested by multiple small accessory spleens,[29] rather than a single, full-sized, normal spleen. Polysplenia sometimes occurs alone, but it is often accompanied by other developmental abnormalities such asintestinal malrotation orbiliary atresia, or cardiac abnormalities, such asdextrocardia. These accessory spleens are non-functional.
Splenic infarction is a condition in which blood flow supply to the spleen is compromised,[30] leading to partial or completeinfarction (tissue death due to oxygen shortage) in the organ.[31]
There has been a long and varied history of misconceptions regarding the physiological role of the spleen, and it has often been seen as a reservoir for juices closely linked to digestion.[35] In various cultures, the organ has been linked tomelancholia, due to the influence ofancient Greek medicine and the associated doctrine ofhumourism, in which the spleen was believed to be a reservoir for an elusive fluid known as "black bile" (one of the four humours).[35] The spleen also plays an important role intraditional Chinese medicine, where it is considered to bea key organ that displays theYin aspect ofthe Earth element (its Yang counterpart is the stomach). In contrast, theTalmud (tractate Berachoth 61b) refers to the spleen as the organ oflaughter while possibly suggesting a link with the humoral view of the organ.
Etymologically,spleen comes from theAncient Greekσπλήν (splḗn), where it was the idiomatic equivalent ofthe heart in modern English.Persius, in his satires, associatedspleen with immoderate laughter.[36] The nativeOld English word for it ismilt, now primarily used for animals; aloanword fromLatin islien.
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.[37]
The spleen, as a byword for melancholy, has also been considered an actual disease.[38] In the early 18th century, the physicianRichard Blackmore considered it to be one of the two most prevalent diseases in England (along withconsumption).[38] In 1701,Anne Finch (later, Countess of Winchilsea) had published aPindaric ode,The Spleen, drawing on her first-hand experiences of an affliction which, at the time, also had a reputation of being a fashionablyupper-class disease of the English.[39] Both Blackmore andGeorge Cheyne treated this malady as the male equivalent of "the vapours", while preferring the morelearned terms "hypochondriasis" and "hysteria".[38][40][41] In the late 18th century, theGerman wordSpleen came to denoteeccentric and hypochondriac tendencies that were thought to be characteristic of English people.[36]
The spleen is one of the many organs that may be included inoffal. It is not widely eaten as a principal ingredient, but cow spleen sandwiches are eaten inSicilian cuisine.[42] Chicken spleen is one of the main ingredients ofJerusalem mixed grill.[43]
Laparoscopic view of a horse's spleen (the purple and grey mottled organ)
Incartilaginous andray-finned fish, the spleen consists primarily of red pulp and is normally somewhat elongated, as it lies inside theserosal lining of theintestine. In manyamphibians, especiallyfrogs, it has the more rounded form and there is often a greater quantity of white pulp.[44]
Inreptiles, birds, andmammals, white pulp is always relatively plentiful, and in birds and some mammals the spleen is typically rounded, but it adjusts its shape somewhat to the arrangement of the surrounding organs. In most vertebrates, the spleen continues to produce red blood cells throughout life; only in mammals this function is lost in middle-aged adults. Many mammals have tiny spleen-like structures known ashaemal nodes throughout the body that are presumed to have the same function as the spleen.[44] The spleens of aquatic mammals differ in some ways from those of fully land-dwelling mammals; in general they are bluish in colour. Incetaceans andmanatees, they tend to be quite small, but in deep divingpinnipeds, they can be massive, due to their function of storing red blood cells.
Marsupials have y-shaped spleens, and it develops postnatally.[45][46][47][48]
The only vertebrates lacking a spleen are thelampreys andhagfishes (the early-branchingCyclostomata, orjawless fishes). 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 presumedhomologous with the spleen of higher vertebrates.[44]
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^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.ISBN978-0-07-146633-2.
^Chow, Kai Uwe; Luxembourg, Beate; Seifried, Erhard; Bonig, Halvard (2016). "Spleen Size Is Significantly Influenced by Body Height and Sex: Establishment of Normal Values for Spleen Size at US with a Cohort of 1200 Healthy Individuals".Radiology.279 (1):306–13.doi:10.1148/radiol.2015150887.ISSN0033-8419.PMID26509293.
^Lodin-Sundström, Angelica; Schagatay, Erika (June 2010). "Spleen contraction during 20 min normobaric hypoxia and 2 min apnea in humans".Aviation, Space, and Environmental Medicine.8 (6):545–49.doi:10.3357/ASEM.2682.2010.PMID20540444.
^abcStanley Eric (2002). "Polysemy and synomyny and how these concepts were understood from the eighteenth century onwards in treatises, and applied dictionaries of English". In Coleman J, McDermott A (ed.).Historical dictionaries and historical Dictionary Research: Papers from the international conference on historical lexicography and lexicology, at the University of Leicester, 2002. Germany: Walter de Gruyter. pp. 170–171.ISBN978-3-11-091260-9.
^Rogers KM (1989). "Finch's "Candid Account" vs. Eighteenth–Century Theories of the Spleen".Mosaic: A Journal for the Interdisciplinary Study of Literature.22 (1):17–27.ISSN0027-1276.JSTOR24780450.
^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,ISBN978-0-8201-1281-7
^abcRomer, Alfred Sherwood; Parsons, Thomas S. (1977).The Vertebrate Body. Philadelphia: Holt-Saunders International. pp. 410–11.ISBN978-0-03-910284-5.
^Old JM, Selwood L, Deane EM (2004). "A developmental investigation of the liver, bone marrow and spleen of the stripe-faced dunnart (Sminthopsis macroura)".Developmental and Comparative Immunology.28 (4):347–355.doi:10.1016/j.dci.2003.08.004.
