- Lymph nodes are small, bean-shaped structures that serve as critical checkpoints in the lymphatic system and play an essential role in the body’s immune defense. They are distributed widely throughout the body, typically found in clusters in regions such as the neck, armpits, chest, abdomen, and groin.
- Each lymph node acts as a filtration and surveillance station, where lymph, a clear fluid containing immune cells, cellular waste, and potential pathogens, is filtered and examined by specialized immune cells.
- Structurally, a lymph node is enclosed by a fibrous capsule and internally divided into an outer cortex and an inner medulla. The cortex contains densely packed lymphoid follicles, which house B lymphocytes. Some of these follicles develop germinal centers during active immune responses, where B cells proliferate and differentiate into plasma cells that produce antibodies. The paracortex, located just below the cortex, is rich in T lymphocytes and dendritic cells. These dendritic cells present foreign antigens to T cells, triggering a cell-mediated immune response.
- Lymph enters the node through afferent lymphatic vessels and flows through a network of channels known as sinuses, where it is exposed to resident macrophages and lymphocytes. These immune cells scan the lymph for foreign particles such as bacteria, viruses, and cancer cells. The medulla contains medullary cords filled with plasma cells, macrophages, and lymphocytes, and it is the final area lymph passes through before exiting the node via efferent lymphatic vessels. This filtration process helps prevent pathogens from entering the bloodstream and spreading systemically.
- Lymph nodes are also sites of antigen presentation and immune cell activation. When a foreign antigen is detected, immune cells within the node become activated, multiply, and initiate an adaptive immune response. This often causes the node to swell, a condition known as lymphadenopathy, which is a common sign of infection or, in some cases, immune disorders or cancer. Swollen lymph nodes are especially noticeable in superficial areas like the neck or under the jaw.
- Functionally, lymph nodes are vital for maintaining immune surveillance, filtering lymph, and coordinating immune responses. They help trap and destroy harmful microorganisms and abnormal cells before they can reach vital organs. In cases of cancer, malignant cells can metastasize through the lymphatic system, making lymph nodes important diagnostic tools for cancer staging and prognosis. Biopsies of affected nodes can reveal the presence of metastatic cells or help diagnose conditions like lymphoma.
