Final answer:
The spleen is the major secondary lymphoid organ that filters pathogens and worn-out red blood cells from the blood.
Step-by-step explanation:
The spleen is the major secondary lymphoid organ in the body. It is located in the upper left quadrant of the abdomen near the stomach and left kidney. The spleen functions to filter pathogens and worn-out red blood cells from the blood. Lymphocytes in the spleen destroy these pathogens and cells.