Lymphoid organs (Organs of the Immune System)

Lymphoid organs (Organs of the Immune System)
The lymphoid system is the part of the immune system comprising a network of ducts called lymphatic vessels that carry a clear fluid called lymph (from Latin lympha "water") unidirectionally toward the heart. The lymphoid system is composed of the organs that produce lymphocytes (bone marrow and thymus), and organs largely composed of lymphoid tissue (lymph nodes, spleen, and the tonsils of the pharyngeal lymphoid ring). Mature lymphocytes are naive when they leave the primary lymphoid organs (bone marrow and thymus). Immunological reactions are initiated by the presentation of antigens to lymphocytes by antigen-presenting cells within secondary lymphoid organs or mucosa-associated lymphoid tissues.
Lymphoid tissue associated with the lymphatic system is concerned with immune functions in defending the body against the infections and spread of tumors. The lymphoid system has multiple interrelated functions; it is responsible for the removal of interstitial fluid from tissues. It transports white blood cells to and from the lymph nodes into the bones. The lymph transports antigen-presenting cells (APCs), such as dendritic cells, to the lymph nodes where an immune response is stimulated.
Lymphoid tissues:
The lymphoid tissue may be primary or secondary, depending upon the stage of lymphocyte development and maturation it is involved in:
A. Primary lymphoid organs
The central (generative) or primary lymphoid organs generate lymphocytes from immature progenitor cells, and where lymphocytes first express