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thumbnail spleen h&e 4x thumbnail spleen h&e 10x
thumbnail spleen h&e 20x thumbnail spleen h&e 40x

Lymphatic tissues in the mice are spleen, lymph nodes, thymus, and gut-associated lymphatic tissue (GALT). GALT includes Peyer’s patches in the gut and the diffuse lymphatic tissue in the gastrointestinal tract and respiratory system; mice have no tonsils. The spleen consists of parenchyma (white and red pulp) covered by a connective tissue capsule that extends into the parenchyma forming septa. Blood vessels enter and leave the parenchyma via the capsule and septa. The white pulp contains the lymphocytes of the spleen, which are organized in periarteriolar lymphocyte sheaths (PALS) around arterioles leaving the septa. The PALS is mostly diffuse lymphatic tissue but usually contains germinal centers, which are highly ordered B-cell clones. The marginal zone with low cell density forms the periphery of the white pulp. The red pulp is the site of life-long, extramedullary hematopoiesis in the mouse and consists of reticular tissue (reticular fibers and reticulocytes) and venous sinuses. In addition to hematopoietic cells, the red pulp contains macrophages, which phagocytize aged erythrocytes, thereby releasing hemosiderin. Accumulation of hemosiderin is mostly seen in multiparous females. Accessory splenic tissue may be found in the pancreas.

The 4X micrograph of the spleen shows the capsule, white and red pulp, and a germinal center and the marginal zone wihin the white pulp.a germinal center. The 10X, and 20X micrographs show the white and red pulp in increasing detail. The 40X micrograph demonstrates the various cells present in the red pulp.

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