The lungs are covered by a thin tissue layer called The visceral pleura which it encloses completely except at the hilum where it is reflected over the structures entering the lung and becomes continuous with the parietal layer. A thin layer of fluid acts as a lubricant allowing the lungs to slip smoothly as they expand and contract with each breath.The parietal pleura lines the interior of the chest wall and upper surface of the diaphragm. Both layers are smooth and shiny and moistened by serous fluid, which acts as a lubricant so that the 2 surfaces glide smoothly over each other during
