Spleen

About the Spleen

The spleen is the largest lymphoid organ, approximately 12 cm long and 150 to 200 grams, located in the left upper quadrant protected by ribs 9 through 11. It has two main functions reflected in its tissue: red pulp 75 percent filters blood, removing old approximately 120 days and damaged red blood cells via splenic macrophages, and holding a reserve of blood cells and platelets that can be released after hemorrhage. White pulp 25 percent is lymphoid tissue organized around central arteries, containing T cell zones PALS and B cell follicles, initiating immune responses to blood borne pathogens. The marginal zone between red and white pulp captures antigens. The spleen recycles iron from hemoglobin through macrophages to transferrin for transport to bone marrow. Accessory spleens spleniculi occur in 10 percent of people and can cause recurrence after splenectomy for ITP. The spleen is not essential for life, but asplenia increases susceptibility to encapsulated organisms pneumococcus, meningococcus, H influenzae, which is why vaccination against these organisms is a standard part of care for people without a functioning spleen. Splenomegaly occurs in mononucleosis, portal hypertension, hematologic malignancies, and Gaucher disease.