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Back to Topics<<<< The spleen is the largest mass of lymphoid tissue in the body, which weighs about 75- 150g in normal adults. It is situated between the fundus of the stomach and diaphragm in the line of tenth rib. Spleen is in contact with the adrenal gland, the upper pole of the kidney, the pancreas and splenic flexure of the colon. It is oval in shape and develops in the dorsal mesogastrium. The spleen has attached with ligaments, of these one ligament stretches between it and the stomach anteriorly called gastrosplenic ligament (Omentum), which contains short gastric and gastroepiploic vessels. Other ligament is situated posteriorly which extends from the spleen backwards to the posterior abdominal wall, where the left kidney is located hence called leinorenal ligament. The splenic vessels that are main pedicles of spleen lie between the layers of leinorenal ligament. Third is the splenocolic ligament. If there is evidence of splenomegaly the additional vascularity of the abovementioned ligaments may be stated. About 15-30%, the evidence of accessorial splenic tissue (accessory spleen) may be present in the following order. Hilus of spleen, gastrosplenic, splenocolic and gastrocolic ligaments. Anteriorly: the stomach, tail of pancreas and left colic flexure. The left kidney lies along its medial border. Posteriorly: the diaphragm, left pleura (left costodiaphragmatic recess), left lung, 9th, 19th and 11th ribs Blood supply: Arterial blood supply comes from the splenic artery which is the branch of the celiac artery. It is tortuous and runs along the upper border of pancreas and then divides into six branches, which enter the hilum of spleen. Venous drainage: Splenic vein comes out of the splenic hilum, runs behind tail and body of pancreas and near the neck of pancreas. It joins superior mesenteric vein to form the portal vein. Lymph drainage: The lymph vessels emerge from hilum and pass through a few lymph nodes along the course of splenic artery and drains into celiac nodes Nerve supply: The nerves to spleen accompany the splenic artery, which are derived from celiac plexus. Accessory spleens are found in the pelvis of women, in the scrotum where it is juxtapositioned with testicles. The spleen has 1.2cm thick capsule and parenchyma. The parenchyma is divided into three parts:
Thus white pulp is the site for vascularization and arterial branching, the marginal zone is the site for lymphocytic infiltration and red pulp contains sinuses. The blood from sinuses drains into splenic vein which creates the main splenic vein. This splenic vein is the most important part of the portal system. The venous pressure in the sinuses actually represents the pressure in the portal system. Functions of spleen: Galen was the first to describe the anatomy of spleen and co-spleens as the organ of the obscure functions. The spleen is intimately connected with three important systems:
Haematopoietic function: Spleen is the site for red cell formation in foetus. This function becomes abeyance after birth, but may sometime resume till the adult life if red bone marrow is extensively destroyed by tumours or replaced by fibrous tissue. Haematoblastic function: As it is the most important member of the reticulo-endothelial system, the spleen is the principal site of the destruction of blood cells of all types. Mean survival of erythrocytes in blood is about 105-120 days. After the damages in the erythrocytes membrane especially biochemical changes contribute to the erythrocyte degeneration in the spleen. The spleen is capable of removal of nuclear remnants such as Howell Jolly bodies, and sideropanic granules from circulating erythrocytes. The neutrophils are removed from the circulation after six hours and platelets in normal circumstances after 10 days. Reservoir function: Big spleen may contain a good proportion of blood volume. The capsule and trabeculae of spleen, rich in plain muscle fibre can contract actively in response to certain stimuli e.g. exercise, asphyxia, haemorrhage etc. to meet the demand for sudden increase in the circulating blood. Defensive activity: Spleen possesses strong phagocytic properties. Foreign bodies coming in contact with phagocytic cells of splenic pulp are quickly removed from blood stream, favoured by the sluggish flow of blood through sinusoids, allowing foreign particles to come in close contact with phagocytes. Spleen also protect against infections as spleen has largest aggregation of lymphoid tissue in body. Metabolic functions: Spleen takes active share in the metabolism of blood pigments. It is closely related to the metabolism of iron storage. Hormone function: There is evidence that spleen secretes a hormone that inhibits the production of thrombocytes and leucocytes by bone marrow. According to some pathologists, an access of this hormone is the cause of thrombocytopaenic purpura and splenic neutropenia. This article has been written by Dr. M. Javed Abbas. If you have any comments please do not hesitate to sign my Guest Book. 21:06 21/12/2002 |
