The area shown here, near the hilar region of the node, shows part of a lymph nodule (LN), the cortical sinus (CS) just below the capsule (Caps), and some of the medullary sinus (MS). Both the cortical sinus and the medullary sinus are spanned by reticular cells (RC). These cells wrap around the collagen cuboidal. The high endothelial venule is identified by its endothelium, which is composed of cells that are cuboidal. A cross-sectioned profile of a postcapillary venule is shown in the inset at higher magnification (×700). The endothelial cell nuclei are round and are lightly stained, in contrast to the nuclei of the surrounding lymphocytes, which are of similar size and shape but are densely stained. This vessel also shows three lymphocytes (arrows) that are in the process of migrating through the wall of the vessel. The lower right corner of this figure reveals a region where there is a considerably lesser concentration of lymphocytes. This area, part of the medulla, contains spaces that represent medullary sinuses (MS).
bundles that form the supporting trabecular framework of the node. The inset reveals the boxed area at higher magnification (×530). The nuclei of the reticular cells (RC) are larger and less densely staining than the lymphocyte nuclei, which are round and densely stained. In H&E preparations, these characteristics allow for the distinction between the reticular cell and the lymphocyte.
KEY A, artery Cap, capillary Caps, capsule CS, cortical sinus LN, lymph nodule MS, medullary sinus HEV, high endothelial venule RC, reticular cells V, vein Val, valve Ven, venule arrowheads, endothelial cells of postcapillary venule arrows, Top image endothelial cells of HEV; Bottom image opening of medullary sinus to lymph vessel
The spleen is the largest lymphatic organ; it is surrounded by a capsule and located in the path of the bloodstream (splenic artery and vein). The spleen filters the blood and reacts immunologically to blood-borne antigens. It has both morphologic and immunologic filtering functions. The substance of the spleen, the splenic pulp, consists of red pulp and white pulp, so named because of their appearance in fresh tissue. The white pulp is rich in lymphocytes that form a periarterial lymphatic sheath (PALS) around branches of the splenic artery that penetrate the white pulp. The red pulp contains large numbers of red blood cells that it filters and degrades. Aged, damaged, or abnormal red blood cells are trapped by macrophages associated with unusual vascular sinuses in the red pulp. These macrophages break down the red cells, begin the metabolic breakdown of hemoglobin, and retrieve and store the iron from the heme for reutilization in the formation of new red blood cells in the bone marrow.
Spleen, human, H&E ×65.
This low-magnification micrograph of the spleen reveals its two major components, the red pulp (RP) and white pulp (WP). In the center of the figure, there is a trabecula containing a blood vessel, a trabecular vein (TV) through which blood leaves the organ. The red pulp constitutes the greater bulk of the splenic tissue. In life, the red pulp has pulp-like texture; it is red as a result of the natural coloration of the numerous red blood cells present, hence its name.
The white pulp, on the other hand, is so named because its content of lymphocytes appears in life as whitish areas. In tissue sections, however, the nuclei of the closely packed lymphocytes impart an overall blue-staining
Red pulp, spleen, human, H&E ×160.