The superficial plexus lies beneath the visceral pleura and drains the surface of the lung and then drains into the bronchopulmonary nodes. The bronchopulmonary nodes drain out of the hilum into the tracheobronchial nodes and then into the bronchomediastinal lymph trunks. The lungs are surrounded by the ribcage. The ribcage and associated muscles facilitate expansion of the lungs for inspiration and the relaxation required for expiration. These two repeated actions serve to refresh the air in the lungs to permit efficient gaseous exchange.
Inspiration is achieved by expansion of the ribcage and lowering of the diaphragm.
Ribcage expansion is usually achieved by the action of the scaleni muscles of the neck and the intercostal muscles. Expiration is usually facilitated by elastic recoil, but under stressful situations forced expiration, involving the quadratus lumborum, serratus posterior and latissimus dorsi takes place.