Lymph Nodes
- Secondary organs of the immune system. These small bean-shaped structures are found where blood and lymph vessels converge, such as the axillary and groin areas.
Overview of Structures:
Capsule
- Gives rise to trabeculae, which divide the node into sections and provide passage for blood vessels.
- Pierce the capsule to deliver lymphatic fluid to the node; valves promote unidirectional flow.
- Area of indentation of the node; the efferent lymphatic vessel drains lymph from the node at the hilum.
- Blood vessels also enter and exit at the hilum.
- Open to the hilum
- Lies just beneath the capsule.
Stroma
Reticular fibers and cells
Lymphatic tissues of Lymph Node
- Lymphatic tissues are responsible for filtering and processing antigens present in the lymphatic fluid as it travels from the afferent vessels to the efferent vessel.
- Lymphatic tissues are densely packed in the cortex
- Reside more loosely in the medulla as the medullary cords.
Cortex
- Outer cortex
- Aggregations of B cells form primary follicles.
- When the B cells proliferate, they produce secondary follicles, which comprise a lighter-staining germinal center and the darker-staining mantle.
- The light and dark areas reflect lymphocyte size: the germinal centers comprise active medium-sized loosely organized lymphocytes, and the mantle comprises smaller lymphocytes with condensed chromatin.
- In addition to lymphocytes, macrophages and follicular dendritic cells (FDC) reside within the follicles;
- Inner cortex
- T cells and dendritic cells
Sinuses and Medullary cords
- Macrophages
- Additional lymphocytes
Route of lymph fluid through Sinuses
- Sinuses are lined by endothelial cells