spleen contains two major units: white pulp and red pulp.[2] The white pulp is composed of lymphatic tissue surrounding a central arteriole and contains mainly white blood cells that are involved in the initiation of the adaptive immune response.Splenic cords lead to splenic sinuses where macrophages respond to antigens and filter abnormal or aging erythrocytes out of blood flow.[4]

A thin, fibrous capsule covers the spleen from which trabeculae arise.Trabeculae are fibrous bands transporting blood vessels to and from the splenic pulp.[5]