Lymph Nodes: Structure, Function, and Components

Anatomy

• Capsule: Dense connective tissue; trabeculae extend inward.
• Cortex (outer): Lymphoid follicles (B-cell zones) with germinal centers.
• Paracortex: T-cell zone (high endothelial venules for lymphocyte entry).
• Medulla (inner): Medullary cords (plasma cells, macrophages, B cells) and sinuses.

Cellular Components

• Lymphocytes: B cells (follicles), T cells (paracortex)
• Macrophages / dendritic cells: Antigen presentation, phagocytosis
• Follicular dendritic cells: Antigen display to B cells
• Reticular cells: Stromal support, cytokine production

Lymph Flow

Afferent lymphatics → subcapsular sinus → cortical sinuses → medullary sinuses → efferent lymphatic (at hilum).

Function

• Filter lymph (trap pathogens, particles, tumor cells)
• Initiate adaptive immune response (antigen presentation, lymphocyte activation)
• Generate memory cells and plasma cells (antibody production)

Clinical Significance

Lymphadenopathy (enlargement) signals infection, inflammation, or malignancy. Biopsy or fine-needle aspiration may be needed for diagnosis.