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The pleura is a membrane that surrounds the lungs of mammals. Presumably, the phrase means that the surface of the pleura was found to be normal in an examination.
The skin surface is not large enough for big creatures such as humans; therefore we have structures in our lungs that greatly increase the surface area.
If the surface area of the organism is small, then there is no problem with getting all the oxygen needed. If the surface area of the organism is large, therefore a special respiratory surface is needed. An example is lungs, gills. The ratio of surface area to volume in a small organism is greater than the ratio in a large organism.
The surface area of the alveoli is where oxygen and carbon dioxide are exchanged across membranes. A large surface area enables a greater amount of gas transfer. The skin has two main functions: one is holding all our bits in one place and the other is to maintain body temerature. In the latter role, a large surface area is good for cooling the body but bad for keeping warm. So it is a compromise.