Human lungs. Anatomical artwork of the human lungs and respiratory system. The heart (which has been removed here) is located between the lungs. At top is the cartilage (blue) of the voicebox and trachea (windpipe), leading down to the lungs. The trachea splits into the bronchi that supply air to each lung. At left, the cutaway section shows the airways (bronchioles) that get smaller and smaller as they branch off from the bronchi. They eventually end in alveoli (yellow), air sacs where gaseous exchange of oxygen and carbon dioxide with the blood occurs. This oxygenated blood is then passed to the heart and pumped around the body.