[Functional morphology of the spleen]

The spleen was till the first half of the twentieth century considered to represent an organ of no special significance. Nowadays its clearance function and position in the immunity system is thoroughly investigated. Informations on its cellular composition and compartments are sufficient. The problems coinciding with circulation in the spleen are solved. The study of interactions of T and B lymphocytes regarding the development of humoral immunity do not provide clear results. Unclear remain also the relations of extracellular and cellular structures. The localisation of the spleen in blood circulation and large amount of migrating lymphocytes justify its significant position in the protection of host against infections spreading haematogenously. It is not inevitable for survival, but its removal increases the risk of unmanageable infections carried by bacteria with polysaccharide capsules. The microenvironment in the spleen enables intercellular relations and determines the development of immune reactions. Microcirculation enables it to function as a biological filter without the necessity of specialized filtrating structures being present. In consequence of blood filtration everything leaks into the extravasal space. Subsequently all components normally constituting the blood return back into the blood within vessels. That is why no special structures are formed in order to filter individual components from the blood. All components that should not be present in the blood are excluded extravasally. The substances which are not let through the wall of sinuses into the blood, remain in the marginal zone and in the red pulp. The macrophages of the marginal zone and red pulp destroy and degrade the unrequired substances. (Ref. 26).