Name the primary and secondary lymphoid organs .

Explanation

Primary lymphoid organs consist of immature lymphocytes differentiate to mature antigen sensitive lymphocytes and after maturation, lymphocytes migrate to secondary lymphoid organs.
Bone marrow is the main lymphoid organ where all the blood cells including lymphocytes are produced. It is the site of B-lymphocytes maturation.
Thymus is a lobed organ located near the heart and beneath the breast bone. It is large at the time of birth, but with age, the size keeps on decreasing and becomes very small on attaining puberty. Growth and maturation of T-lymphocytes takes place here.
Secondary lymphoid organs provide the sites for the interaction of lymphocytes with the antigen, which then proliferate to become effector cells. The secondary lymphoid organs are as follow.
Spleen is a large bean shaped organ containing lymphocytes, phagocytes and large number of erythrocytes. It filters the blood by trapping blood borne microorganisms.
Lymph nodes are small structures located at different points along the lymphatic system. Their function is to trap the microorganism or other antigens that enter the lymph and tissue fluid. The trapped antigens in the lymph nodes are responsible for the activation of lymphocytes present there and cause the immune response.
Mucosal Associated Lymphoid Tissue is located within the lining of major tracts in the body like respiratory, digestive, urogenital tracts. MALT constitutes about 50% of the lymphoid tissue in human body.