ABSTRACT
THE PLEURA The pleura is a fibroelastic serous membrane lined by squamous epithelium forming a sac on each side of the chest. Each pleural sac is a closed cavity invaginated by a lung. Parietal pleura lines the chest wall and visceral (pulmonary) pleura covers the lungs. These two pleural layers are continuous around the root of the lung and are separated by a thin film of serous fluid, permitting them to glide easily on each other. The layers are prevented from separating by the fluid’s surface tension and the negative pressure in the thoracic cavity. Thus, when the thoracic cage expands, the lung also must expand and air is inhaled.
