spleen (redirected from Spleen disorders)

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.

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spleen

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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spleen

1. a spongy highly vascular organ situated near the stomach in man. It forms lymphocytes, produces antibodies, aids in destroying worn-out red blood cells, and filters bacteria and foreign particles from the blood

2. the corresponding organ in other animals

3. Archaic another word for melancholy

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spleen [splēn]

(anatomy)

A blood-forming lymphoid organ of the circulatory system, present in most vertebrates.

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Spleen

An organ of the circulatory system present in most vertebrates, lying in the abdominal cavity usually in close proximity to the left border of the stomach.

In humans the spleen normally measures about 1 by 3 by 5 in. (2.5 × 7.5 × 12.5 cm) and weighs less than ½ lb (230 g). It is a firm organ with an oval shape and is indented on its inner surface to form the hilum, or stalk of attachment to the peritoneum. This mesentery fold also carries the splenic artery and vein to the organ.

The spleen is an important part of the blood-forming, or hematopoietic, system; it is also one of the largest lymphoid organs in the body and as such is involved in the defenses against disease attributed to the reticuloendothelial system. Although the chief functions of the spleen appear to be the production of lymphocytes, the probable formation of antibodies, and the destruction of worn-out red blood cells, other less well-understood activities are known. For example, in some animals it may act as a reservoir for red blood cells, contracting from time to time to return these cells to the bloodstream as they are needed. In the fetus and sometimes in later life, the spleen may be a primary center for the formation of red blood cells. Another function of the spleen is its role in biligenesis. Because the spleen destroys erythrocytes, it is one of the sites where extrahepatic bilirubin is formed. See Bilirubin