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                 Lymphoid organs of the body

 Lymphoid organs :  These are the organs where origin and or maturation and proliferation of lymphocytes occur. (a) The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into sensitive lymphocytes.

 (1) Bone marrow : Bone marrow present in bones is the main lymphoid organ where all bllod cells including lyphocytes are produced. Bone marrow provides the microenvironment for the development and maturationof B lymphocytes.

(2) Thymus : Thymus is a lobeled organ located near the heart and beneath the breast bone. Thymus is quite large at the time of birth but keeps reducing withg age and by the time puberty is attained ity atrophies to a very small size. It provides microenvironment for the development and maturation of T- lymphocytes.


(b)  Secondary lymphoid organs : The lymphocytes after maturation migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Payer's pathes of small intestine and appendix. The secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells.

(1) Spleen : Spleen is a large bean shaped organ. It is organised into white pulp and red pulp. It mainly contains lymphocytes and phagocytes. It acts as a filter nof the blood by trapping blood- born microorganisms. Spleen also has a large reservoir of erythrocytes.

 (2) Lymph nodes : Lymph nodes serve to trap the microorganisms or other antigens, which happen to get into the lymph and tissue fluid . Antigens trapped in the aymph nodes are responsible for the activation of lymphocytes present there ans call forth the immune response.

 (3) Mucosal - associated lymphoid tissues: Lymphoid tissue located within the lining of the major tracts is mucosal- associated lymphoid tissue. It constitutes about 50% of the lymphoid tissue in human body.

 (4) The lymphoid tissue of the gut is called gut associated lymphoid tissue . they are called Peyer's patches.








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