Lungs are spongy, grayish-pink organs present in the chest. It remains the center piece of the respiratory system. When a person breathes in, air enters the lungs and oxygen from that air moves into the blood. At the same time, carbon dioxide moves from the blood into the lungs and is exhaled. This process is called gas exchange. The respiratory system also includes the trachea, muscles of the chest wall, diaphragm, blood vessels and other tissues.