This figure reveals, at a higher magnification, the red pulp and a portion of the trabecular vein from the area enclosed in the uppermost rectangle in top figure. The red pulp is composed of two elements: venous sinuses (VS) and the splenic cords (of Billroth), the tissue that lies between the sinuses. In this speci men, the venous sinuses can be seen to advantage because the red blood cells in the sinuses have lysed and appear as unstained “ghosts”; only the nuclei of the white cells are readily seen. (This is better shown in Plate 40.) The paler, unstained areas thus represent the sinus lumina.
response. The lymphatic tissue that constitutes the white pulp differs from nodules seen elsewhere in that it follows and ensheathes a blood vessel, the central artery. The lymphatic tissue surrounding the artery exhibits periodic expansion, thus forming the nodules. When this occurs, the central artery (CA) is displaced peripherally within the nodule.
In those regions where the lymphatic tissue is not in nodular form, it is present as a thin cuff around the central artery and is referred to as the periarterial lymphatic sheath. If the plane of section does not include the artery, the sheath may appear only as a localized and irregular aggregation of lymphocytes.
Near the top of the micrograph, two venous sinuses (arrows) empty into the trabecular vein (TV), thus showing the continuity between venous sinuses and the trabecular veins. The wall of the vein is thin, but the trabecula (T) containing the vessel gives the appearance of being part of the vessel wall. In humans as well as in other mammals, the capsule and the trabeculae that extend from the capsule contain myofibroblasts. Under conditions of increasing physical stress, contraction of these cells will occur and cause rapid expulsion of blood from the venous sinuses into the trabecular veins and, thus, into the general circulation.
White pulp, spleen, human, H&E ×240.
This figure reveals, at higher magnification, the splenic nodule in the rectangle in the right portion of figure above. Present are a germinal center (GC) and a cross section through the thick-walled central artery (CA). As noted above, the central artery is eccentrically placed in the nodule. The marginal zone (MZ) is the area that separates white pulp and red pulp (RP). Small arterial vessels and capillaries, branches of the central artery, supply the white pulp, and some pass into the reticular network of the marginal zone, terminating in a funnel-shaped orifice. Venous sinuses are also found in the marginal zone, and occasionally, arterial vessels may open into the sinuses. The details of the vascular supply are, at best, difficult to resolve in typical H&E preparations. The penicillar arterioles, the terminal branches of the central artery, supply the red pulp but are likewise difficult to resolve.
KEY CA, central artery GC, germinal center MZ, marginal zone RP, red pulp T, trabecula TV, trabecular vein VS, venous sinus WP, white pulp arrows, venous sinuses emptying into the trabecular vein
Red pulp, spleen, human, H&E, ×360.
As previously noted, the red pulp consists of the venous sinuses (VS) and the area between the venous sinuses, the splenic cords (of Bilroth) (SC). In this specimen, the red blood cells have been lysed leaving only a clear outline of the individual cells. Thus, the relatively clear spaces with scattered nuclei represent the lumen of the venous sinus; the nuclei are those of white blood cells. When the wall of a venous sinus is tangentially sectioned (VW), as in this figure, the endothelial cells, which are rod-like in shape, appear as a series of thin, linear bodies.
Red pulp, spleen, human, H&E, ×1,200.