|The spleen serves two major functions in the body: 1. It is responsible for the destruction of old red blood cells (RBC), 2. It is a major site for mounting the immune response. The spleen behaves similar to a lymph node but instead of filtering the lymphatic fluid it filters the blood. Blood entering the spleen travels through progressively smaller arterioles until it is deposited in an area known as the red pulp. This is where the RBCs are processed. Surrounding each of the arterioles is a sheath of lymphoid cells which make up the periarteriolar lymphoid sheath (PALS). The interface between the PALS and the blood is a region of intense phagocytic activity and sets the stage for an immune response. The immune reactivity of the spleen is especially effective for dealing with blood-borne antigens such as bacteria that reach the blood.|
Histological Cross Section of the Spleen
Red Pulp: Clusters of Macrophages and Red Blood Cells.
White Pulp: Lymphocytes suspended on reticular Fibers