Final answer:
Each cortical nodule in lymphoid tissues contains a less dense area known as the germinal center, which is important for the formation of lymphocytes and the adaptive immune response.
Step-by-step explanation:
Each cortical nodule is composed of packed lymphocytes that surround a less dense area called the germinal center. This is an anatomical structure in the lymph node where part of the immune response is organized. Lymphoid nodules are key components of the immune system and are found in lymphoid tissues such as the lymph nodes, the spleen, and in mucosal-associated lymphoid tissue throughout the respiratory and digestive tracts. The germinal centers within these nodules are crucial for the formation of lymphocytes. They contain rapidly dividing B cells that are surrounded by a layer of T cells and other accessory cells, which are vital for adaptive immune responses mediated by these lymphocytes.