Immunology | Immune system| Immunity

           A number of morphologically and functionally diverse organs and tissues have various functions in the develpoment of immune responses.These can be distinguished by functions as the primary and secondary lymphoid organs.The thymus and bone marrow are the primary(or central) lymphoid organs,where maturation of lymphocytes takes place.The lymph nodes,spleen,and various mucosal-associated lymphoid tissue(MALT) such as gut-associated lymphoid tissue(GALT) are the secondary (or peripheral)lymphoid organs,which trap antigen and provide sites for mature lymphocytes to interact with that antigen.In addition,tertiary lymphoid tissues,which normally contain fewer lymphoid cells than secondary lymphoid organs,can import lymphoid cells during inflammatory response.Most prominent of these are cutaneous-associated lymphoid tissues.Once mature lymphocytes have been generated in the primary lymphoid organs,they circulate in the blood and lymphatic system,a network of vessels that collect fluid that has escaped into the tissues from capillaries of the circulatory system and ultimately return it to blood.