The structures of the Spleen includes:

In terms of circulation, branches of the splenic artery enter the white pulp from the trabeculae, become central arteries. They then continue to the red pulp, where they branch into several straight arterioles called penicillar arterioles. Some are surrounded by macrophages, which are called sheathed capillaries. They empty directly into the meshwork of the red pulp (open circulation). In the other model, sheathed capillaries open directly into the splenic sinus (closed circulation). Experimental and morphologic evidence supported the open circulation model as it has more efficient exposure of red cells to the macrophages of the red pulp.