Lymph Node Anatomy

Lymph Node Tissues

The anatomy of a lymph node is organized to facilitate the filtering and processing of lymphatic fluid, as well as the initiation of immune responses. Here’s a description of the key components:

1. Capsule: A lymph node is encapsulated by a dense connective tissue capsule, which provides structural support and defines the boundary of the node.
2. Afferent lymphatic vessels: Lymphatic fluid enters the lymph node through afferent lymphatic vessels, bringing in antigens and immune cells from peripheral tissues.
3. Cortex: The cortex is the outer region of the lymph node and is divided into two main areas:
   • B cell follicles (nodules): These are spherical structures within the cortex where B cells predominantly reside. Within the B cell follicles, you can find germinal centers where B cells proliferate, differentiate, and undergo somatic hypermutation and class switching. Follicular dendritic cells (FDCs) are also present in the germinal centers, providing a supportive microenvironment for B cell activation and antibody production.
   • Subcapsular sinus: Adjacent to the subcapsular region, the cortex also contains areas where antigen-presenting cells, such as dendritic cells and macrophages, reside.
4. Paracortex: The paracortex is the region between the cortex and the medulla and is primarily composed of T cells. It contains high endothelial venules (HEVs), which are specialized blood vessels that allow lymphocytes to enter the lymph node from the bloodstream. The paracortex is a site of T cell activation and proliferation.
5. Medulla: The medulla is the innermost region of the lymph node. It contains medullary cords, which consist of plasma cells, B cells, macrophages, and antibody-producing cells. The medulla also contains medullary sinuses, which are interconnected spaces that drain lymphatic fluid towards the efferent lymphatic vessels.
6. Efferent lymphatic vessels: Lymphatic fluid exits the lymph node through efferent lymphatic vessels, carrying filtered lymphatic fluid and immune cells to downstream lymph nodes or back into circulation.

Overall, the anatomy of a lymph node is highly organized to facilitate the capture and processing of antigens, the activation and proliferation of immune cells, and the generation of adaptive immune responses.

Common Cells within Different Lymph Node Tissues

1. Subcapsular region:
   • Macrophages: Responsible for capturing and processing antigens that enter the lymph node via afferent lymphatic vessels.
   • Dendritic cells: Present in the subcapsular region to capture antigens and initiate immune responses.
2. Cortex:
   • B cells: Predominantly found in B cell follicles, where they participate in antigen recognition, activation, and differentiation into plasma cells.
   • Follicular dendritic cells (FDCs): Present in germinal centers of B cell follicles to support B cell activation and affinity maturation.
   • T cells: Some T cells can be found in the cortex, particularly around the periphery of B cell follicles.
3. Paracortex:
   • T cells (primarily CD4+ and CD8+ T cells): Abundant in the paracortex, where they undergo activation and proliferation in response to antigens presented by dendritic cells and other antigen-presenting cells.
   • High endothelial venules (HEVs): Specialized blood vessels present in the paracortex that facilitate the entry of lymphocytes from the bloodstream into the lymph node.
4. Medulla:
   • Plasma cells: Found in medullary cords, where they produce antibodies in response to antigens encountered in the lymph node.
   • Macrophages: Present in the medullary cords to phagocytose antigens and support antibody production.
   • B cells: Some B cells may migrate to the medulla, particularly plasma cell precursors.
   • Dendritic cells: Can be found in the medulla, involved in antigen presentation and immune regulation.
   • Efferent lymphatic vessels: Not a cell type, but efferent lymphatic vessels are part of the medullary region and facilitate the drainage of lymphatic fluid from the lymph node.

These cell types work together within the different tissues of the lymph node to mount effective immune responses against pathogens and foreign antigens.

Next Topic: “Crowd Surfing” Particulate Antigens Are Shuttled to B Cells in Lymph Node Follicles

Source: ChatGPT response prompted and edited by Joel Graff.

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