Lymph node: cortex, paracortex, medulla !
- Organ
Lymph nodes are bean-shaped filters along lymph vessels where B and T cells meet antigens carried in from the tissues.
Updated 2026-11-01
See it in 3D: Neck lymph nodes · Mesenteric lymph nodes · Superficial inguinal nodes · Mediastinal lymph nodes
What it is
A lymph node is a small encapsulated secondary lymphoid organ that filters lymph on its way back to the blood. Dendritic cells bring antigen from the tissues, and naive lymphocytes arrive from the blood, so this is where most adaptive responses start. Each zone has a job: B cells in the cortex, T cells in the paracortex, and plasma cells and macrophages in the medulla.
Structure
- Fibrous capsule with trabeculae and a reticular-fiber mesh that holds the cells.
- Outer cortex with round follicles; deeper paracortex; inner medulla near the hilum.
- Sinuses lined by macrophages slow the lymph so antigens can be caught.
Step by step
- Lymph from a tissue enters through afferent vessels with free antigen and migrating dendritic cells.
- Dendritic cells settle in the paracortex and present antigen to naive T cells.
- Activated helper T cells move to the follicle edge and help B cells that found the same antigen.
- B cells form a germinal center, multiply and improve antibody affinity.
- Plasma cells move to the medullary cords and release antibody into the efferent lymph.
Clinical notes
- Reactive lymphadenopathy: tender, mobile nodes during infection in the area they drain.
- Hard, fixed, painless or growing nodes raise concern for metastasis or lymphoma.
- Tuberculous lymphadenitis (scrofula) is a common cause of chronic neck nodes in Colombia and Latin America.
- Breast cancer usually spreads first to the axillary nodes; the sentinel node is the first one that drains the tumor.
- A left supraclavicular node can be the first sign of an abdominal cancer, such as stomach cancer.
Test yourself
Think of the answer, then tap the question to see it.
In which zone of the lymph node are T cells concentrated?
In the paracortex, between the cortical follicles and the medulla.
What are high endothelial venules for?
They are specialized venules in the paracortex where naive lymphocytes leave the blood and enter the node.
Where are plasma cells found in a lymph node?
In the medullary cords.
Which nodes does breast cancer usually reach first?
The axillary lymph nodes; the first one draining the tumor is called the sentinel node.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Primary and secondary lymphoid organs
- Dendritic cell (professional antigen-presenting cell)
- B cell and plasma cell
- CD4⁺ helper T cell
- B-cell activation, class switching and affinity maturation
Related conditions
Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.
Sources: 21.1 Anatomy of the Lymphatic and Immune Systems (OpenStax, Rice University (Anatomy and Physiology 2e), 2022); Dendritic Cells (British Society for Immunology, 2024).
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Representative model, for educational purposes only.