A Scanning Electron Microscopic Study of the Spleen

The reticulum and vascular sinuses of the normal rat spleen were studied by scanning electron microscopy. Observations were also made of erythrocytes, macrophages, platelets, and other migratory elements. Reticular cells of the periarterial lymphatic sheath, the marginal zone, and cordal spaces were large, bulky, irregular cells with broad processes that formed a spongework. When marked retraction of these cells was induced in the drying phase of tissue preparation, they showed the slender multiple fingerlike processes characteristic of the argyrophilic reticulum. The reticular cells at the periphery of the periarterial lymphatic sheath were flattened and formed cylinders about the central artery. They were, moreover, associated with unusually heavy extracellular fibers. Vascular sinuses were suspended in the reticulum by attachments of cordal reticular cells and of fibrillar reticulum to the adventitial surface. Adventitial cells of the sinus, moreover, branched into the cords. Endothelial cells typically lay side by side without gaps, except as migratory cells passed through the wall. Erythrocytes were commonly observed in passage across the sinus wall. In sinuses and cords, they were often swollen, irregular, and bore blebs and crenulations. Macrophages displayed rich surface folds and processes. Platelets were abundant and were adherent to the surface of reticular cells and the endothelium of sinuses. Such adherence appeared to be the manner in which the platelets were sequestered in the spleen.