The human spleen is located in the upper left abdomen, behind the stomach
|System||Immune system (Lymphatic system)|
The spleen is an organ found in virtually all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes from Ancient Greek σπλήν (splḗn).
The spleen plays important roles in regard to red blood cells (erythrocytes) and the immune system.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 red blood cells (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.
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. These monocytes, upon moving to injured tissue (such as the heart after myocardial infarction), turn into dendritic cells and macrophages while promoting tissue healing.The spleen is a center of activity of the mononuclear phagocyte system and is analogous to a large lymph node, as its absence causes a predisposition to certain infections.
In humans the spleen is purple in color and is in the left upper quadrant of the abdomen.
The spleen is underneath the left part of the diaphragm, 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 posterior renal 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 the stomach. Below this it is in contact with the tail of the pancreas. 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 left adrenal gland.
|155–159 cm||6.4–12 cm|
|160–164 cm||7.4–12.2 cm||8.9–11.3 cm|
|165–169 cm||7.5–11.9 cm||8.5–12.5 cm|
|170–174 cm||8.3–13.0 cm||8.6–13.1 cm|
|175–179 cm||8.1–12.3 cm||8.6–13.4 cm|
|180–184 cm||9.3–13.4 cm|
|185–189 cm||9.3–13.6 cm|
|190–194 cm||9.7–14.3 cm|
|195–199 cm||10.2–14.4 cm|
The spleen, in healthy adult humans, is approximately 7 centimetres (2.8 in) to 14 centimetres (5.5 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 9th and 11th ribs on the left-hand side and along the axis of 10th rib. The weight varies between 1 oz (28 g) and 8 oz (230 g) (standard reference range), correlating mainly to height, body weight and degree of acute congestion but not to sex or age.
Near the middle of the spleen is a long fissure, the hilum, which is the point of attachment for the gastrosplenic ligament and the point of insertion for the splenic artery and splenic vein. There are other openings present for lymphatic vessels and nerves.
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.
The germinal centers are supplied by arterioles called penicilliary radicles.
The spleen is innervated by the splenic plexus, which connects a branch of the celiac ganglia to the vagus nerve.
The underlying central nervous processes coordinating the spleen's function seem to be embedded into the Hypothalamic-pituitary-adrenal-axis, and the brainstem, especially the subfornical organ.
The spleen is unique in respect to its development within the gut. While most of the gut organs are endodermally derived (with the exception of the neural-crest derived adrenal gland), the spleen is derived from mesenchymal tissue.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.
|red pulp||Mechanical filtration of red blood cells. In mice: Reserve of monocytes|
|white pulp||Active 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:
Enlargement of the spleen is known as splenomegaly. It may be caused by sickle cell anemia, sarcoidosis, malaria, bacterial endocarditis, leukemia, pernicious anemia, Gaucher's disease, leishmaniasis, Hodgkin's disease, Banti's disease, hereditary spherocytosis, cysts, glandular fever (mononucleosis or 'Mono' caused by the Epstein–Barr virus), and tumours. Primary tumors 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 (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 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.
Traumas, such as a road traffic collision, can cause rupture of the spleen, which is a situation requiring immediate medical attention.
Asplenia refers to a non-functioning spleen, which may be congenital, or caused by traumatic injury, surgical resection (splenectomy) or a disease such as sickle cell anaemia. Hyposplenia refers to a partially functioning spleen. These conditions may causea modest increase in circulating white blood cells and platelets, a diminished response to some vaccines, and an increased susceptibility to infection. In particular, there is an increased risk of sepsis from polysaccharide 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 by IgM memory B cells (a subtype of B cells) in the marginal zone of the spleen.
A splenectomy (removal of the spleen) results in a greatly diminished frequency of memory B cells.A 28-year follow-up of 740 World War II veterans whose spleens were removed 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 (41 rather than the expected 30), but not from other conditions.
An accessory spleen is a small splenic nodule extra to the spleen usually formed in early embryogenesis. Accessory spleens are found in approximately 10 percent of the populationand are typically around 1 centimeter in diameter. Splenosis is a condition where displaced pieces of splenic tissue (often following trauma or splenectomy) autotransplant in the abdominal cavity as accessory spleens.
Polysplenia is a congenital disease manifested by multiple small accessory spleens,rather than a single, full-sized, normal spleen. Polysplenia sometimes occurs alone, but it is often accompanied by other developmental abnormalities such as intestinal malrotation or biliary atresia, or cardiac abnormalities, such as dextrocardia. These accessory spleens are non-functional.
Splenic infarction is a condition in which blood flow supply to the spleen is compromised, leading to partial or complete infarction (tissue death due to oxygen shortage) in the organ.
Splenic infarction occurs when the splenic artery or one of its branches are occluded, for example by a blood clot. Although it can occur asymptomatically, the typical symptom is severe pain in the left upper quadrant of the abdomen, sometimes radiating to the left shoulder. Fever and chills develop in some cases.It has to be differentiated from other causes of acute abdomen.
The spleen may be affected by hyaloserositis, in which it is coated with fibrous hyaline.
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.
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.William Shakespeare, in Julius Caesar uses the spleen to describe Cassius's irritable nature.
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 French 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 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 apply to both males and females. Similarly, the English term "splenetic" describes a person in a foul mood.
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. Sanhedrin 21b and Avodah Zarah 44a (and Rashi ibid.) additionally describe how in the ancient world, some runners destroyed their spleens with drugs to increase their speed, and hollowed out the soles of their feet of flesh so as not to feel thorns and thistles as they ran.
The spleen also plays an important role in traditional Chinese medicine and is the Yin part of the Earth element paired with its Yang counterpart the Stomach.
In German "einen Spleen haben" means to be quirky or eccentric, to have a strange but usually not harmful habit. In German the meaning of "spleen" changed in the mid 19th century from "being melancholy" to "being eccentric".
In cartilaginous and ray-finned fish, it consists primarily of red pulp and is normally somewhat elongated, as it lies inside the serosal lining of the intestine. In many amphibians, especially frogs, it has the more rounded form and there is often a greater quantity of white pulp.. A study published in 2009 using mice found that the red pulp of the spleen forms a reservoir that contains over half of the body's monocytes.
In reptiles, birds, and mammals, white pulp is always relatively plentiful, and in birds and 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 as haemal nodes throughout the body that are presumed to have the same function as the spleen.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 massive, due to their function of storing red blood cells.
The only vertebrates lacking a spleen are the lampreys and hagfishes (the Cyclostomata). 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 homologous with the spleen of higher vertebrates.
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 to assist wound healing.
The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the circulatory system and the immune system. It is made up of a large network of lymphatic vessels, lymphatic or lymphoid organs, and lymphoid tissues. The vessels carry a clear fluid called lymph towards the heart.
A lymph node, or lymph gland is a kidney-shaped organ of the lymphatic system, and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that include B and T cells. Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles including cancer cells, but have no detoxification function.
A splenectomy is the surgical procedure that partially or completely removes the spleen.
Monocytes are a type of leukocyte, or white blood cell. They are the largest type of leukocyte and can differentiate into macrophages and myeloid lineage dendritic cells. As a part of the vertebrate innate immune system monocytes also influence the process of adaptive immunity. There are at least three subclasses of monocytes in human blood based on their phenotypic receptors.
Infarction is tissue death (necrosis) due to inadequate blood supply to the affected area. It may be caused by artery blockages, rupture, mechanical compression, or vasoconstriction. The resulting lesion is referred to as an infarct (from the Latin infarctus, "stuffed into").
Asplenia refers to the absence of normal spleen function and is associated with some serious infection risks. Hyposplenism is used to describe reduced ('hypo-') splenic functioning, but not as severely affected as with asplenism.
Splenomegaly is an enlargement of the spleen. The spleen usually lies in the left upper quadrant (LUQ) of the human abdomen. Splenomegaly is one of the four cardinal signs of hypersplenism which include: some reduction in number of circulating blood cells affecting granulocytes, erythrocytes or platelets in any combination; a compensatory proliferative response in the bone marrow; and the potential for correction of these abnormalities by splenectomy. Splenomegaly is usually associated with increased workload, which suggests that it is a response to hyperfunction. It is therefore not surprising that splenomegaly is associated with any disease process that involves abnormal red blood cells being destroyed in the spleen. Other common causes include congestion due to portal hypertension and infiltration by leukemias and lymphomas. Thus, the finding of an enlarged spleen, along with caput medusae, is an important sign of portal hypertension.
An autosplenectomy is a negative outcome of disease and occurs when a disease damages the spleen to such an extent that it becomes shrunken and non-functional. The spleen is an important immunological organ that acts as a filter for red blood cells, triggers phagocytosis of invaders, and mounts an immunological response when necessary. Lack of a spleen, called asplenia, can occur by autosplenectomy or the surgical counterpart, splenectomy. Asplenia can increase susceptibility to infection. Autosplenectomy can occur in cases of sickle-cell disease where the misshapen cells block blood flow to the spleen, causing scarring and eventual atrophy of the organ. Autosplenectomy is a rare condition that is linked to certain diseases but is not a common occurrence. It is also seen in systemic lupus erythematosus (SLE).
Primary myelofibrosis (PMF) is a rare bone marrow blood cancer. It is classified by the World Health Organization (WHO) as a type of myeloproliferative neoplasm, a group of cancers in which there is abnormal growth of cells in the bone marrow. This overproduction is most often associated with a somatic mutation in the JAK2, CALR, or MPL gene markers. In PMF, the healthy marrow is replaced by scar tissue (fibrosis), resulting in a lack of production of normal blood cells. Symptoms include anemia, increased infection and an enlarged spleen (splenomegaly).
Warm antibody autoimmune hemolytic anemia (WAIHA) is the most common form of autoimmune haemolytic anemia. About half of the cases are of unknown cause, with the other half attributable to a predisposing condition or medications being taken. Contrary to cold autoimmune hemolytic anemia which happens in cold temperature (28–31 °C), WAIHA happens at body temperature.
Extramedullary hematopoiesis refers to hematopoiesis occurring outside of the medulla of the bone. It can be physiologic or pathologic.
Felty's syndrome, also called Felty syndrome, (FS) is rare autoimmune disease characterized by the triad of rheumatoid arthritis, enlargement of the spleen and too few neutrophils in the blood. The condition is more common in those aged 50–70 years, specifically more prevalent in females than males, and more so in Caucasians than those of African descent. It is a deforming disease that causes many complications for the individual.
Kurloff cells were described as mononuclear cells in the peripheral blood and organs of the guinea pig, capybara, paca, agouti and cavie. The Kurloff cell contains a characteristic proteoglycan-containing inclusion body. In the guinea pig, Kurloff cells are more numerous in the adult female than the adult male. A marked increase in the number of circulating Kurloff cells is present in the peripheral blood during pregnancy and after estrogen treatment in male and female animals. A relatively smaller number of cells take place in immature, non-pregnant, and non-estrogen-treated animals. The exact function of Kurloff cells remains unknown, but it has some of the characteristics of both monocytes and lymphocytes. In guinea-pigs, it has been proposed that Kurloff cells mainly involve in the function of the immune system, such as acting as a natural killer cell and preventing damage to the trophoblast by maternal defensive cells. Also, Kurloff cells present antibody-dependent cytotoxic activity in vitro.
White pulp is a histological designation for regions of the spleen, that encompasses approximately 25% of splenic tissue. White pulp consists entirely of lymphoid tissue.
The red pulp of the spleen is composed of connective tissue known also as the cords of Billroth and many splenic sinusoids that are engorged with blood, giving it a red color. Its primary function is to filter the blood of antigens, microorganisms, and defective or worn-out red blood cells.
Splenic infarction is a condition in which blood flow supply to the spleen is compromised, leading to partial or complete infarction in the organ.
Spleen transplantation is the transfer of spleen or spleen fragments from one individual to another. It is under research for induction of immunological tolerance for other transplanted organs. Success has been achieved in rodent models. Recently, evidence has been obtained for a tolerogenic effect of a spleen transplant in miniature swine (Frank JMF Dor, PhD thesis). Also, the spleen harbors primitive hematopoietic progenitor cells. Spleen transplantation surgery has been performed on humans with mixed results.
An accessory spleen is a small nodule of splenic tissue found apart from the main body of the spleen. Accessory spleens are found in approximately 10 percent of the population and are typically around 1 centimetre in diameter. They may resemble a lymph node or a small spleen. They form either by the result of developmental anomalies or trauma. They are medically significant in that they may result in interpretation errors in diagnostic imaging or continued symptoms after therapeutic splenectomy. Polysplenia is the presence of multiple accessory spleens rather than one normal spleen.
B-cell prolymphocytic leukemia, referred to as B-PLL, is a rare blood cancer. It is a more aggressive, but still treatable, form of leukemia.
White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from multipotent cells in the bone marrow known as hematopoietic stem cells. Leukocytes are found throughout the body, including the blood and lymphatic system.
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