Pathways of pleural liquid turnover

Schematic representation of the pathways of normal pleural liquid turnover. Pleural liquid appears to originate from the systemic vessels of both the parietal and visceral pleural membranes (dashed arrows). The parietal vessels (intercostal microvessels) are thought to be of primary importance because they are closer to the pleural space and have a higher filtration pressure than the bronchial microvessels of the visceral pleura. Pleural liquid is initially partially reabsorbed by the microvessels; the remaining fluid exits the pleural space via the lymphatic stomata in the parietal pleura (solid arrow).