Final answer:
Large lymph capillaries spanned by reticular fibers in a lymph node are called lymph sinuses.
Step-by-step explanation:
Lymph sinuses are expansive lymph capillaries found in the medulla of lymph nodes, forming a network supported by crisscrossing reticular fibers. These sinuses serve as crucial conduits for lymph, the fluid that transports immune cells and debris through the lymphatic system. Macrophages line the walls of these sinuses, creating a filtration system within the lymph node. As lymph traverses these sinuses, macrophages capture and process foreign particles, antigens, and damaged cells. This filtration process enhances the immune response by removing potential threats and promoting the activation of lymphocytes. Ultimately, the cleansed lymph exits the node through efferent lymphatic vessels, continuing its journey through the body.