Lymph Nodes (LN)
Lymph Nodes (LN): Structure, Function, and Clinical Significance
Structure and Location
Lymph nodes (LN) are small, bean- or kidney-shaped organs, typically 1–2 cm in size, and are distributed throughout the body, with adults having approximately 800 nodes. They are most commonly located in the neck, axilla (armpits), thorax, abdomen, and groin, often at the convergence of major blood vessels25.
Each lymph node is encapsulated by dense connective tissue, which sends trabeculae (internal extensions) into the node, creating a lobular structure. The node has an indentation called the hilum, where arteries and veins enter and exit, and where efferent lymphatic vessels leave the node5.
Internal Anatomy
- Afferent lymphatic vessels bring lymph fluid into the node from peripheral tissues.
- Subcapsular sinus lies just beneath the capsule and receives lymph from afferent vessels2.
- Cortex: The outer layer, rich in B-cells (arranged in follicles), and contains a germinal center for B-cell activation. The paracortex (inner cortex) is T-cell rich and is where T-cells interact with antigen-presenting dendritic cells25.
- Medulla: The innermost region, containing medullary cords (with plasma cells, B-cells, macrophages) and medullary sinuses, which drain filtered lymph toward the efferent vessel2.
- Efferent lymphatic vessels exit at the hilum, returning filtered lymph to the venous circulation5.
Function
Lymph nodes are secondary lymphoid organs and play a central role in the immune system. Their primary functions include:
- Filtering lymph: Lymph nodes filter interstitial fluid (lymph) collected from tissues, trapping pathogens, foreign particles, and cancer cells2.
- Immune surveillance: They provide a site for antigen presentation to lymphocytes. B-cells and T-cells are exposed to antigens with the help of dendritic cells and follicular dendritic cells, facilitating both innate and adaptive immune responses25.
- Activation of lymphocytes: When exposed to antigens, B-cells in the cortex can form germinal centers and proliferate, while T-cells in the paracortex become activated to coordinate immune responses2.
Clinical Relevance
- Enlarged lymph nodes (lymphadenopathy) can indicate infection, immune response, or malignancy. Nodes are considered abnormal if persistently enlarged, lose their oval shape, or show asymmetrical cortical thickening12.
- Pathways of spread: Lymph nodes are crucial in cancer staging, as many cancers spread via the lymphatic system.
- Drainage patterns: Specific groups of lymph nodes drain particular regions of the body (e.g., cervical nodes for the head and neck, axillary nodes for the upper limb and breast, inguinal nodes for the lower limb and perineum)2.
Summary Table: Key Features of Lymph Nodes
| Feature | Description |
|---|---|
| Shape/Size | Bean/kidney-shaped, 1–2 cm, encapsulated |
| Main Regions | Cortex (B-cells), Paracortex (T-cells), Medulla (plasma cells, macrophages) |
| Blood Supply | Artery and vein enter/exit at the hilum |
| Lymph Flow | Afferent vessels → subcapsular sinus → cortex/paracortex → medulla → efferent vessel |
| Function | Filter lymph, antigen presentation, lymphocyte activation |
| Clinical Significance | Infection, cancer spread, immune response |
Lymph nodes are essential hubs of immune activity, filtering lymph and orchestrating immune responses to pathogens, cancer cells, and other foreign substances25.
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References:
A detailed review of normal lymph node structure, internal compartmentalization, and immune function is provided in “Normal Structure, Function, and Histology of Lymph Nodes” (DOI: 10.1080/01926230600867727)1.
The article “Lymph nodes in health and disease – A pathologist’s perspective” discusses lymph node anatomy, zonation, immune roles, and clinical significance in disease (DOI: 10.4103/jomfp.jomfp_40_23)3.
“New tools for immunologists: models of lymph node function from cells to tissues” reviews the spatial organization, immune cell distribution, and functional dynamics of lymph nodes (DOI: 10.3389/fimmu.2023.1183286)
