Introduction
The spleen is a significant organ of the hematologic and reticuloendothelial systems. It is an intraperitoneal organ located in the left upper quadrant of the abdomen posterior and lateral to the stomach.[1] The spleen is situated anatomically behind the 9 and 11 ribs on the left side of the body.
Cellular Level
The 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. The innermost area of the white pulp, the germinal center, contains B-cells while the surrounding marginal zone contains T-cells.[3] The marginal zone is surrounded by a periarteriolar lymphoid sheath (PALS), which also contains T-cells. White pulp throughout the spleen is surrounded by red pulp. The red pulp is composed of splenic cords (Cords of Billroth) and a large volume of venous sinuses, which gives the structure its characteristic red appearance under a microscopic. The splenic cords provide the organ structure through reticulin and fibrils. The cords also contain a reservoir of monocytes to aid in wound healing. 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]