Spleen

The spleen is an organ that is not essential for life. It can be divided into the red pulp, consisting of sinuses lined by macrophages, and the white pulp which is similar in structure to lymphoid follicles.

There are at least four functions that the spleen undertakes:

• sequestration and phagocytosis of aged red cells:
  • red cells pass through the red pulp of the spleen
  • aged or abnormal red cells are phagocytosed
    
    
• immunological:
  • the spleen is the largest single organ of the immune system
  • macrophages within the spleen can remove antibody coated red cells and bacteria from the blood
    
    
• blood reservoir:
  • up to one third of platelets are sequestrated in the spleen
  • in addition, an enlarged spleen can accommodate a significant proportion of the circulating red cell mass
    
    
• extramedullary haemopoiesis:
  • the spleen is an organ of haemopoiesis in the foetus
  • it also undertakes this role in adult life at times of haemopoietic stress e.g. haemolytic anaemia, thalassaemia and myelofibrosis

A spleen only becomes palpable on examination when it is approximately three times its normal size.