[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Immunology](https://durgical.com/en/immunology/) › [Lymphoid organs](https://durgical.com/en/immunology/#a-organs) › Lymph node: cortex, paracortex, medulla [Immunology](https://durgical.com/en/immunology/) · [Lymphoid organs](https://durgical.com/en/immunology/#a-organs) # 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](https://durgical.com/en/anatomy/lymph-nodes-of-neck/) · [Mesenteric lymph nodes](https://durgical.com/en/anatomy/superior-mesenteric-nodes/) · [Superficial inguinal nodes](https://durgical.com/en/anatomy/superficial-inguinal-nodes/) · [Mediastinal lymph nodes](https://durgical.com/en/anatomy/mediastinal-lymph-nodes/) ## Key points - Afferent lymph vessels enter through the capsule into the subcapsular sinus; efferent vessels leave at the hilum. - Cortex: B-cell follicles; activated (secondary) follicles have germinal centers. - Paracortex: T cells and dendritic cells; naive lymphocytes enter from the blood through high endothelial venules. - Medulla: medullary cords (plasma cells, macrophages) and medullary sinuses that drain to the efferent vessel. - Paracortex is poorly developed in DiGeorge syndrome; follicles are scarce in B-cell deficiencies such as X-linked agammaglobulinemia. ## 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. ## Memory aid Read the node from outside in like a letter: B on the envelope (cortex), T inside the fold (paracortex), and the plasma-cell signature at the bottom (medulla). ## 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. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/immunology/lymph-node-cortex-paracortex-medulla/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [Neck lymph nodes](https://durgical.com/en/anatomy/lymph-nodes-of-neck/) - [Mesenteric lymph nodes](https://durgical.com/en/anatomy/superior-mesenteric-nodes/) - [Superficial inguinal nodes](https://durgical.com/en/anatomy/superficial-inguinal-nodes/) - [Mediastinal lymph nodes](https://durgical.com/en/anatomy/mediastinal-lymph-nodes/) ## Related - [Primary and secondary lymphoid organs](https://durgical.com/en/immunology/primary-and-secondary-lymphoid-organs/) - [Dendritic cell (professional antigen-presenting cell)](https://durgical.com/en/immunology/dendritic-cell/) - [B cell and plasma cell](https://durgical.com/en/immunology/b-cell-and-plasma-cell/) - [CD4⁺ helper T cell](https://durgical.com/en/immunology/cd4-helper-t-cell/) - [B-cell activation, class switching and affinity maturation](https://durgical.com/en/immunology/b-cell-activation-class-switching-and-affinity-maturation/) ## Related conditions - [Cervical lymphadenopathy](https://durgical.com/en/conditions/cervical-lymphadenopathy/) - [Breast cancer](https://durgical.com/en/conditions/breast-cancer/) - [Tuberculosis](https://durgical.com/en/conditions/tuberculosis/) - [Lymphoedema](https://durgical.com/en/conditions/lymphoedema/) [← All of immunology](https://durgical.com/en/immunology/) 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](https://openstax.org/books/anatomy-and-physiology-2e/pages/21-1-anatomy-of-the-lymphatic-and-immune-systems) (OpenStax, Rice University (Anatomy and Physiology 2e), 2022); [Dendritic Cells](https://www.immunology.org/public-information/bitesized-immunology/cells/dendritic-cells) (British Society for Immunology, 2024). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/immunology/lymph-node-cortex-paracortex-medulla/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/immunology/lymph-node-cortex-paracortex-medulla/