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| Normal lymph node | ||
| Etiology •N/A | ||
| Pathogenesis •N/A, | ||
| Epidemiology •N/A | ||
| General Gross Description •Normal lymph nodes are small, bean-shaped structures. •They range in size from 5 mm to 15 mm in greatest dimension. •They gray/white in color in most of the body. •However, the lymph nodes in the mediastinum and in relationship to the lower respiratory tract are flecked with dark gray to black granules due to the inhalation of carbon pigment from urban pollutants and/or smoking. Lymph nodes have a convex surface and a concave surface. •The convex surface is the area through which lymph fluid flows into the lymph node. •The concave surface, at its middle, has a region known as the hilus through which an arteriole and a venule enter and exit respectively. •The efferent lymphatic also leaves the lymph the node at the hilus. •The cut surface may reveal small, grainy prominences, representing lymphoid follicles. •Examples: | ||
| General Microscopic Description •Microscopically, the lymph node is covered for its entire outer surface by a thin fibrous tissue capsule, which is somewhat thicker at the hilus. A low power examination of the lymph node reveals that there is a cortex and a medulla. •Beneath the fibrous tissue capsule is a structure known as the marginal sinus, which is an invert bowl shaped structure. •Afferent lymphatics enter the lymph node through the capsule and drain into the marginal sinus. •The marginal sinus connects with numerous sinuses within the body of the lymph node, all of which ultimately drain into the efferent lymphatic. •The substance of the lymph node is divided into a variable number of compartments by fibrous tissue trabeculae, which are continuous with the capsule. •Between the trabeculae, the substance of the lymph node is supported by fine reticulin fibers and by tissue macrophages. •The rest of the space of the lymph node is occupied by lymphoid cells, including T cells, B cells and plasma cells. •The cortex contains aggregates of lymphocytes. •These aggregates are spherical collections that are barely discernible from the rest of the tissue of the lymph node in a resting lymph node. •In this case, these aggregates are called primary follicles. •Upon antigenic stimulation, primary follicles develop paler staining, germinal centers. •Germinal centers represent active immune response and are pale because of the accumulation of cytoplasm in the proliferating B lymphocytes, as well as an influx of antigen presenting histiocytes and macrophages. •The presence of large, dendritic antigen presenting cells with cell debris is a feature of an active immune response. •In addition, numerous mitotic figures, due to the active replication of B lymphocytes is also a noticeable feature of the germinal center. •Examples: | ||
| Clinical Correlation •N/A | ||
| References Bloom and Fawcett: A textbook of Histology. 12th Edition. Chapman & Hall. 1994. pp 447 Gray: Gray's Anatomy. 15th Edition. Barnes & Noble Books. 1995. pp 62 et seq. Please be patient during transfer. Medline will open in a new window. To return, close the Medline Window Normal lymph node
| Synopsis by: T.V.Rajan, M.D., Ph.D. (T08000M00100)[621]
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