An organ that removes worn-out and defective red blood cells from the circulation and helps to fight infection by producing some of the antibodies, lymphocytes, and phagocytes that destroy invading microorganisms. The spleen is a fist-sized, spongy organ in the upper left abdomen behind the lower ribs.
The spleen enlarges in many diseases.
These include infections such as malaria and infectious mononucleosis; blood disorders such as leukaemia, thalassaemia, and sickle cell anaemia; and tumours such as lymphomas.
Enlargement of the spleen may be accompanied by hypersplenism.
The spleen may be ruptured by a severe blow to the abdomen.
This can cause potentially fatal haemorrhage, and an emergency splenectomy is needed.
The large organ lying to the left of, below, and behind the stomach. This organ is partially responsible for white blood cell formation (red blood cells in childhood), and it is lined with resident macrophages that help it filter the blood, remove and recycle old and dead red blood cells, and send this all up to the liver in the portal blood. The liver, in fact, does most of the recycling of splenic hemoglobin derivatives. The spleen initiates much resistance and immunologic response, being made mostly of lymph pulp, and it stores and concentrates a large number of red blood cells. These can be injected into the bloodstream for immediate use under flight or fight stress, since the spleen is covered with capsule and vascular muscles that constrict in the presence of adrenalin or sympathetic adrenergic nerve stimulus.
An organ deeply placed in the abdomen and a major constituent of the RETICULOENDOTHELIAL SYSTEM.
Position and size The spleen lies behind the stomach, high up on the left side of the abdomen, and corresponds to the position of the ninth, tenth and 11th ribs, from which it is separated by the diaphragm. It is a soft, highly vascular, plum-coloured organ, and has a smooth surface. It is usually about 12·5–15 cm (5–6 inches) in length, and weighs about 170 grams or more. In diseased conditions the organ may reach a weight of 8–9 kg.
Structure The spleen is enveloped by peritoneal membrane beneath which is a strong elastic tunic, composed partly of ?brous tissue
containing many elastic ?bres, and partly of unstriped muscle. This elastic coat allows of the free expansion and contraction of the organ according to the varying amount of blood present in it. From the inner surface of the membrane, ?brous partitions known as trabeculae run down into the substance and form a network in which the dark spleen pulp is contained. The pulp consists of delicate connective-tissue ?bres passing between the various trabeculae, and of white and red blood cells lying in this meshwork. The spleen is very vascular and venous blood leaves by the splenic vein and then enters the portal vein from the liver. There are also numerous lymphatics in the organ, which run in the trabeculae or surround the veins.
Functions The organ produces lymphocytes (see LYMPHOCYTE) and acts as a reservoir of red blood cells for use in emergencies. It is also one of the sites for the manufacture of red blood cells in the fetus, but not after birth. Useless or worn-out red and white blood cells and blood PLATELETS are broken up by this organ. This results in the production of BILIRUBIN, which is conveyed to the liver, and of iron, which is used in the bone marrow for the production of new red blood cells.
n. a large dark-red ovoid organ situated on the left side of the body below and behind the stomach. It is enclosed within a fibrous capsule that extends into the spongy interior – the splenic pulp – to form a supportive framework. The pulp consists of aggregates of *lymphoid tissue (white pulp) within a meshwork of *reticular fibres packed with red blood cells (red pulp). The spleen is a major component of the *reticuloendothelial system, producing lymphocytes in the newborn and containing *phagocytes, which remove worn-out red blood cells and other foreign bodies from the bloodstream. It also acts as a reservoir for blood and, in the fetus, as a source of red blood cells. Anatomical name: lien. —splenic adj.
In certain diseases associated with marked changes in the blood, such as LEUKAEMIA and MALARIA, the SPLEEN becomes chronically enlarged. In some of the acute infectious diseases, it becomes congested and acutely enlarged: for example, in typhoid fever (see ENTERIC FEVER), ANTHRAX and infectious MONONUCLEOSIS. Rupture of the spleen may occur, like rupture of other internal organs, in consequence of extreme violence – but in malarious countries, where many people have the spleen greatly enlarged and softened as the result of malaria, rupture of this organ occasionally occurs following even a light blow to the left side of the abdomen. The spleen, in consequence of its structure, bleeds excessively when torn, so that this accident is generally followed by collapse, signs of internal haemorrhage – and death if not dealt with promptly by operation.... spleen, diseases of
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