How do lymph nodes function as filters?

• A. It releases lymphocytes as part of defence mechanism
• B. Sometime lymph nodes can become overwhelmed and enlarged
• C. All lymph must pass through one lymph node before returning to circulation
• D. Each node monitors for micro-organisms in the lymph and acts as a filter

Answer: (D)

Lymph nodes filter lymph by screening it for pathogens as it travels through the node. Inside, macrophages and other phagocytes capture and destroy microbes, debris, and abnormal cells. Antigen-presenting cells, like dendritic cells, show pieces of these microbes to lymphocytes, helping to activate the immune response. The lymph travels in through afferent vessels, passes through subcapsular and other sinuses where this surveillance happens, and exits via efferent vessels after it has been screened. This filtering helps prevent pathogens from circulating freely and coordinates the body’s defense by activating B and T cells in the node. Lymph nodes can enlarge when this immune activity ramps up, but filtration occurs across multiple nodes along the lymphatic system, not just in one. The idea that lymphocytes are simply released as a primary filtering function isn’t what filtration is about, and while lymph may swell during infection, the essential role of the node is to monitor and filter the lymph content.