[6] In addition to clearing aged red blood cells, the sinusoids also filter out cellular debris, particles that could clutter up the bloodstream.

Red pulp consists of a dense network of fine reticular fiber, continuous with those of the splenic trabeculae, to which are applied flat, branching cells.

The meshes of the reticulum are filled with blood: Macrophages are highly diverse mononuclear phagocytes that are present throughout the body, including the spleen.

From the Billroth's cords, the blood passes into the venous sinuses of the red pulp, which are lined with discontinuous endothelium as well as stress fibres extending under the basal plasma membrane, parallel to the cellular axis.

Also, the erythrocyte can store larger amounts of iron in the form of hemosiderin (an insoluble complex of partially degraded ferritin), and large deposits of this can be seen in the red pulp macrophages.

The red pulp macrophages also obtain iron by scavenging a complex of haemoglobin (released from erythrocytes destroyed intravascularly throughout the body) and haptoglobin, via endocytosis through CD163.