spleen

spleen

[spleen]
spleen, soft, purplish-red organ that lies under the diaphragm on the left side of the abdominal cavity. The spleen acts as a filter against foreign organisms that infect the bloodstream, and also filters out old red blood cells from the bloodstream and decomposes them. These functions are performed by phagocytic cells that are capable of engulfing and destroying bacteria, parasites, and debris. Ordinarily, the spleen manufactures red blood cells only toward the end of fetal life, and after birth that function is taken over by the bone marrow. However, in cases of bone marrow breakdown, the spleen reverts to its fetal function. The spleen also acts as a blood reservoir; during stress or at other times when additional blood is needed, the spleen contracts, forcing stored blood into circulation (see circulatory system). It is sometimes necessary to remove the spleen entirely, particularly in trauma cases, although recent studies have shown the spleen to be far more important than initially suspected in the fight against infection.

Lymphoid organ, located in the left side of the abdomen behind the stomach. The spleen is the primary filtering element for the blood, and it is a storage site for red blood cells (erythrocytes) and platelets. It is one of four places where reticuloendothelial cells are found (see reticuloendothelial system). Two types of tissue, red pulp and white pulp, are intermixed. The white pulp is lymphoid tissue containing lymphocyte production centres. The red pulp is a network of channels filled with blood where most of the filtration occurs and is the major site of destruction of deteriorating erythrocytes and recycling of their hemoglobin. Both contain cells (see leukocyte) that remove foreign material and initiate an antibody-producing process. The spleen becomes enlarged in some infections. Its rupture in high-impact injuries may require surgical removal, which leaves the patient more susceptible to overwhelming infection.

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The spleen is an organ found in all vertebrate animals. In humans, the spleen is located in the abdomen of the body, where it functions in the destruction of redundant red blood cells and holds a reservoir of blood. It is regarded as one of the centers of activity of the reticuloendothelial system (part of the immune system). It is increasingly recognized that its absence leads to a predisposition to certain infections.

Anatomy

The spleen is an organ found in the left upper abdomen above the stomach and underneath the rib cage. Spleens in healthy adults are approximately in length.

Like the thymus, the spleen possesses only efferent lymphatic vessels.

Function

Area Function Composition
red pulp Mechanical filtration. Removes unwanted materials from the blood, including old red blood cells.

white pulp Helps fight infections. Composed of nodules, called Malpighian corpuscles. These are composed of:

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 hematopoeisis 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 and other formed elements. This is only valid for certain mammals, such as dogs and horses. In horses roughly 50% of the red blood cells are stored there. The red blood cells can be released when needed These animals also have large hearts in relation to their body size to accommodate the higher-viscosity blood that results. In humans, however, the spleen does not function as a depository of red blood cells, but instead it stores platelets in case of an emergency. 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.

    Disorders

    Disorders include splenomegaly, where the spleen is enlarged by various reasons. On the other hand, a lack of normal spleen function is called asplenia.

    Etymology and cultural views

    The word spleen comes from the Greek splēn. In Latin its name is lien.

    In French, spleen 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 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 "shplehn," refers to a persisting somewhat eccentric (but not quite lunatic) idea or habit of a person; however the organ is called "Milz", (cognate with Old English milte).

    In 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.

    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", "發脾氣" is used as an expression for getting angry, although in the view of Traditional Chinese Medicine, the view of "脾" does not correspond to the anatomical "spleen".

    In chiropractic (meric chart) problems with the spleen relate to T8 (eighth thorasic vertebrea), a subluxation at T8 is associated with low energy and/or low immune system function.

    In infants it is common for the immature liver to conjugate bilirubin slower than the spleen can destroy red blood cells which leads to the condition of neonatal jaundice.

    See also

    Additional images

    Footnotes

    External links

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