Introduction to Lymph Nodes
Lymph nodes are small, bean-shaped structures that play a crucial role in the immune system. They are found throughout the body and act as filters for foreign particles and cancer cells. Histologically, lymph nodes are composed of various cell types and tissues that facilitate their function in immunity.Anatomy and Structure
Lymph nodes are typically 1-25 mm in diameter and are distributed along the course of lymphatic vessels. They are encapsulated by a fibrous capsule and divided into the cortex and medulla. The cortex contains lymphoid follicles, while the medulla consists of medullary cords and sinuses.Histological Features
Under the microscope, lymph nodes exhibit distinct zones:
- Cortex: Contains primary and secondary lymphoid follicles. Primary follicles are small and contain naïve B cells, while secondary follicles have a germinal center surrounded by a mantle zone.
- Paracortex: Located beneath the cortex and contains T cells and dendritic cells.
- Medulla: Contains medullary cords (rich in plasma cells, macrophages, and B cells) and medullary sinuses (pathways for lymph fluid).Cell Types
Several cell types are found within lymph nodes:
- Lymphocytes: B and T cells are the main immune cells.
- Macrophages: Phagocytose pathogens and present antigens.
- Dendritic Cells: Antigen-presenting cells that activate T cells.
- Reticular Cells: Form the structural framework of the lymph node.Function
Lymph nodes filter lymph fluid, trapping bacteria, viruses, and other foreign substances. They provide a site for immune cell activation and proliferation. Antigens are presented to lymphocytes, initiating an immune response.Pathological Changes
Lymph nodes can undergo various pathological changes:
- Reactive Hyperplasia: Enlargement due to infection or inflammation.
- Lymphadenopathy: General term for swollen lymph nodes.
- Lymphoma: Malignant proliferation of lymphocytes within the node.Histological Examination
Histological examination of lymph nodes involves tissue sectioning, staining, and microscopic analysis. Common stains include Hematoxylin and Eosin (H&E) for general morphology and immunohistochemical stains for specific cell markers.Clinical Significance
Lymph node assessment is crucial in diagnosing infections, autoimmune diseases, and cancers. Biopsies are often performed to examine lymph node architecture and cellular composition.Conclusion
Histology of lymph nodes provides essential insights into their function and role in the immune system. Understanding their structure and cellular composition aids in diagnosing and treating various medical conditions.
