Lymph nodes are small encapsulated organs composed of a dense reticular meshwork ensheathed by stellate reticular cells and lymphoid tissue and cells.
Nodes act as in-series filters for lymph carried in lymphatic vessels.
Each node receives lymph from a limited region, but all lymph must pass through at least one lymph node. Lymph nodes have a cortex and a medulla. Primary follicles differ from secondary follicles in that they do not possess germinal centers. This results in mitoses of lymphocytes and their subsequent differentiation into plasma cells or small B lymphocyte memory cells. The memory B lymphocytes are ultimately located in the mantle zone of secondary follicles and are long-lived.