비장, or the spleen, is an organ located in the upper left part of the abdomen. It plays a crucial role in the immune system by filtering blood and removing old or damaged red blood cells. The spleen also helps produce white blood cells, which are essential for fighting infections. In addition to its immune functions, the 비장 stores blood and helps regulate blood volume in the body. It can release stored blood into the circulatory system when needed, such as during physical exertion or injury. Overall, the spleen is vital for maintaining a healthy immune response and blood balance.