Define primary and secondary lymphoid tissues. how and why do lymphocytes recirculate?

Hematopoietic organ is the producer of blood lines, while lymphoid organ is the organ of lymphocyte production and differentiation. The lymphoid system is composed of lymphoid organs:

- Primary: thymus, bone marrow and Fabrizio bag (birds).

- Secondary: spleen, lymph nodes, lymphoid tissues associated with mucous membranes (MALT) including tonsils, vermiform appendix, Peyer's plaques, adenoids.

Explanation:

PRIMARY OR CENTRAL LINFOID BODIES.

They are lymphopoietic organs in which lymphocytes are differentiated from primary cells, to functional effector cells, through a process of proliferation and maturation. In mammals, they are the thymus, fetal liver and adult bone marrow.

Here, lymphocytes acquire specific antigens to defend themselves against microorganisms and distinguish their own from the non-self.

SECONDARY LINFOID BODIES

They are lymph nodes, spleen and lymphoid tissue associated with mucous membranes. They are places where the necessary environment is created so that lymphocytes can interact with each other, with Ags and CPAs, to give an appropriate immune response.  It also disseminates the immune response.

Continuous recirculation process that lymphocytes undergo between blood and lymphatic circulation, during which they track peripheral lymphoid tissues, in search of the antigen for which they are specific, to once found, recognize it and initiate an immune response that makes its elimination .

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