The lungs have two lymphatic supplies (see figure 15.7). The superficial lymphatic vessels are deep to the visceral pleura; theydrain lymph from the superficial lung tissue and the visceral pleura. The deep lymphatic vessels follow the bronchi; they drain lymph from the bronchi and associated connective tissues. No lymphatic vessels are located in the walls of the alveoli. Both the superficial and deep lymphatic vessels exit the lungs at the main bronchi.
Phagocytic cells within the lungs phagocytize most carbon particles and other debris from inspired air and move them to the lymphatic vessels. In older people, the surface of the lungs can appear gray to black because of the accumulation of these particles, especially if the person smoked or lived primarily in a city with air pollution. Other materials, such as cancer cells from the lungs, can also spread to other parts of the body through the lymphatic vessels.