# The Spleen --- The **spleen** is a secondary [[lymphatic system|lymphatic]] organ that lives in the [[abdominopelvic cavity#Quadrents and Regions|left upper quadrant]] of the abdominal cavity. It's primary function is to filter the [[blood]] to look for any substance there that might trigger an [[immune system|immune response]]. This is also where old and dying [[red blood cells]] and [[platelets]] are removed from circulation and broken down. Functions: - store broken down RBC products for later reuse - site of fetal erythrocyte production (normally ceases after birth) - stores blood platelets - site of lymphocyte proliferation ___