For each of the lymphatic and immune systems explain how one (1) component of each of the organ systems (a cell, tissue, or organ) contributes to the function of either detecting or fighting off an infection. (3 marks each; 6 marks total) Solution Lymphatic system is a closed circulatory system that consists of lymph capillaries, lymph vessels, and lymph nodes. The lymph present in capillaries flows into lymphatic vessels, which are presented deep or superficial. This lymphatic system is mainly involved in the production of \"active and passive immunity\" (components of immune system) against the foreign pathogens entered into the host system. Lymphatic system is going to produce lymphocytes to defend these pathogens by opsonization & finally eliminate them out of the host body. Lymph node is a lymphatic organ where the cleansing of the lymph and activation of T-cells and B-cells will occur. Parenchyma of the lymph node is divided into cortex and medulla. Cortex is the outer part, which is C-shaped and encircles the four-fifth of organ. Cortex contains conical or ovoid shaped lymphatic nodules. Medulla is the inner part, which extends to the surface of hilum. Medullary cords are present in the medulla. This medullary cord consists of lymphocytes, macrophages, plasma cells, reticular fibres and reticular cells. Both the cortex and medulla consists of lymph-filled sinuses, which are continuous with subcapsular sinus. Lymphatic system is a closed circulatory system that consists of lymph capillaries, lymph vessels, and lymph nodes. The lymph present in capillaries flows into lymphatic vessels, which are presented deep or superficial. These lymph vessels combine to form lymphatic trunks that empty into the large collecting vessels of lymphatic system called “thoracic duct and right lymphatic duct.” The lymphoid tissue is mostly composed of a reticular connective tissue (a type of loose connective tissue). The fibres of the reticular network contain macrophages. A number of lymphocytes from the postcapillary venule walls occupy this network and leave to the body again. This ensures the lymphocytes to identify the infected sites at a faster rate. The components of lymphoid tissue include the following. 1). Lymphoid cells: Lymphocytes are produced (lymphopoiesis) by primary lymphoid tissues or organs, which include red bone marrow and thymus gland. These are the main cells of immune system; they mature into two types of immunocompetent cells known as T-lymphocytes and B-lymphocytes contributes to the function of either detecting or fighting off an infection. a). T-lymphocytes: The thymus gland produces “T lymphocytes” (T for thymus) from the lymphoid stem cells under the influence of thymus hormones. The matured T cells (differentiated) are mainly involved in the process of cell-mediated immunity. b). B-lymphocytes: B- Lymphocytes are produced from the red bone marrow and are mainly involved in providing antibody mediated immunity. When these cells .