Human lungs are located in two cavities on either side of the heart. Though similar in appearance, the two aren't identical. Both are separated into lobes by fissures, with three lobes on the right and two on the left. The lobes are further divided into segments and then into lobules, hexagonal divisions of the lungs that're the smallest subdivision visible to the naked eye. The connective tissue that divides lobules's often blackened in smokers and city dwellers. The medial border of the right… (More on Lung)