What are lymph nodes?

• A. Nerve bundles near lymph vessels
• B. Glands that secrete hormones into lymph
• C. Masses of lymphoid tissue situated along the lymphatic vessels
• D. Lymphatic vessels that drain blood

Answer: (C)

Lymph nodes are small, encapsulated masses of lymphoid tissue that lie along the lymphatic vessels. They act as filters for the lymph, trapping bacteria, viruses, and other debris as the fluid passes through. Inside, immune cells such as lymphocytes and macrophages scan for invaders and coordinate immune responses, including the activation and maturation of cells that produce antibodies. Lymph nodes are connected to the lymphatic system by vessels bringing lymph in and taking it away after filtration. They are not nerve bundles, hormone-secreting glands, or lymphatic vessels that drain blood. When a node swells, it usually reflects infection, inflammation, or disease in the area it drains.