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Physiological Functions Of The Spleen, Its Clinical Significance And Disorders
The Sleen In The Human Body
Functions of the spleen
The spleen is made up of collections of lymphocytes in the white pulp perfoming an immune function and reticuloendothelial cells in the red pulp perfoming phagocytic function. The normal spleen weighs 120- 200g.
White Pulp: It serves the following immunological functions:
- Antibodies to circulating antigens are produced
- Probably a factor which increases neutrophil chemotaxis and phagocytosis (tuftsin) is produced. Absence of this factor is possibly responsible for the increased susceptibility to infection in asplenic subjects.
Red Pulp: It serves the following functions:
- Phagocytic functions: The cells of the red pulp remove defected red cells, antibody coated cells and bacteria
- Removal of nuclear remnants, Heinz bodies etc. from erythrocytes.
- The spleen acts as a reservoir for the formed elements of blood and these are released into the general circulation in times of stress.
- Hematopoiesis occurs in the spleen normally in fetal life. When there is impairment of normal marrow activity, the spleen takes up extramedullary hematopoiesis.
Splenomegaly In Status Objectivus
Various conditions lead to splenomegaly in the tropics. Size of the enlarged spleen is variable and when gross, the spleen may fill almost the whole abdomen. An enlarged spleen can sequester up to 25% to 30% of the total red cell mass. In splenomegaly, since the plasma volume is increased and red cells are sequestered, dilutional anemia results. Massive splenomegaly from any cause leads to secondary effects on the hemopoietic tissues known as hypersplenism.
Some of the common causes of splenomegaly are as follows
Chronic infections: Malaria, leishmaniasis, trypanosomiasis, disseminated tuberculosis, brucellosis and systemic mycotic infections. In these conditions, the spleen is considerably enlarged and generally firm in consistency.
Acute infections: Septicemia, enteric fever, viral hepatitis, infectious mononucleosis, infective endocarditis, exanthemata, relapsing fevers and typhus. The spleen is moderately enlarged and often soft.
Venous Congestion: Portal hypertension and chronic right-sided heart failure. In portal hypertension, spleen assumes large sides.
Hematological neoplasia: Leukemias, lymphomas, polycythemia vera, essential thrombocythemia and myelofibrosis.
Reactive splenomegaly with reticuloendo thelial hyperplasia: Hemolytic anemias, megaloblastic anemia, thalassemias and hemoglobinopathies, myelophthisic conditions, tropical splenomegaly and acquired hypogammaglobulinemia.
Granulomatous disorders: Felty’s syndrome, systemic lupus erythematosus, sarcoidosis and berylliosis.
Infiltrative disorders: Lipid storage disease, amyloidosis, histiocytosis-X and gargoylism.
Hypersplenism In A Patient
This condition is characterized by the occurrence of anemia, leucopenia and thrombocytopenia occurring in a patient with moderate or gross splenomegaly. The bone marrow is active and hypercellular. The pancytopenia clears promptly on splenectomy. The pancytopenia is probably due to splenic sequestration and destruction of cells and also probably due to a humoral factor depressing cell maturation.
Hypersplenism may be primary with no detectable cause or secondary. Secondary hypersplenism is more common. In such cases, splenomegaly is usually secondary to portal hypertension, hepatic, portal or splenic vein thrombosis, lymphomas, tropical splenomegaly, malaria, Kala azar, myeloproliferative disorders, tuberculosis, sarcoidosis or hemolytic anemias.
Treatment: In primary hypersplenism, splenectomy improves the blood picture. The functional role of the spleen can be assessed by isotopic tests.
Tropical splenomegaly syndrome
Also known as the big spleen disease or African macroglobulinemia or Cryptogenic splenomegaly. This refers to the condition reported from Africa, New Guinea and India of persistent splenomegaly without evidence of any underlying cause. In India, maximum number of cases have been reported from Bengal. The spleen shows normal capsule and hyperplasia of the lymphoid follicles and Kupffer cells. Portal hypertension may develop.
The condition is characterized by gross splenomegaly and lymphocytic infiltration of hepatic sinusoids. The titer of malarial antibodies (IgM) is high but malarial pigment is absent from the liver or spleen.
The disease is seen in early life. The clinical picture is dominated by massive splenomegaly. Anemia and signs of hypersplenism. If left untreated, 30-50% patients die in 6 years.
Treatment: Continuous antimalarial treatment with proguanil 100 mg/day, over several months may help to reduce the splenic size in some cases. Splenectomy is indicated if there is hypersplenism.
Asplenic Patient With Infections
This term is used to denote the condition that develops after splenectomy or after splenic atrophy. Minor alterations of cellular and humoral immunity may be encountered.
- Asplenia may be congenital or may develop as the result of splenectomy. Congenital asplenia may be accompanied by fatal cardiovascular anomalies.
- Splenic atrophy may result from infarction, injury or irradiation. Around 30% of adult celiac disease are associated with splenic atrophy. Rarely ulcerative colitis and Crohn’s disease may also be associated with splenic atrophy.
Hematological features: Erythrocytes show the presence of large number of target cells and Howell-Jolly bodies. Moderate leukocytosis and thrombocytosis are present.
Complications: Septicemias due to streptococcus pneumonia, Hemophilus influenza and meningococcai are common, children being more susceptible. Protozoal infections such as malaria, babesiosis and toxoplasmosis are more common.
Management: Asplenic subjects should receive early and effective bactericidal drug therapy at the first sign of infection. Pneumococcal vaccine is available for active immunization of susceptible subjects.
When the platelet count exceeds 400,000/cmm, it is called thrombocytosis. Thrombocytosis is usually temporary. In contrast to this, sustained elevation of platelet count above 800,000/cmm is characteristic of thrombocythemia.
Thrombocytosis accompanies several conditions like hemorrhage, surgery, splenectomy, splenic vein thrombosis, disseminated carcinoma, Hodgkin’s disease, tuberculosis, ulcerative colitis, acute rheumatic fever, etc. thrombocytosis is usually not associated with symptoms unless the platelet count is very high. On the other hand, hemorrhage or thrombosis may occur in thrombocythemia.
© 2014 Funom Theophilus Makama