Final answer:
Spherical clusters of lymphocytes and macrophages in the lymphatic system are called lymphoid nodules. These nodules are involved in the immune response by presenting antigens to lymphocytes, especially in areas exposed to pathogens.
Step-by-step explanation:
Spherical clusters of lymphocytes and macrophages found throughout the lymphatic system are called lymphoid nodules. Lymphoid nodules, unlike lymph nodes, do not have a surrounding fibrous capsule. They are involved in the immune response, as they are densely packed with lymphocytes that can respond to pathogens. These nodules are often found in areas of the body that are routinely exposed to environmental pathogens, such as the respiratory and digestive tracts.
Lymphoid nodules play a critical role in presenting antigens to lymphocytes and are integral to the function of lymph nodes, which house a large population of B and T cells, as well as dendritic cells and macrophages that present antigens and help to mount an immune response against pathogens.