Serous Membranes line the trunk cavities and cover the organs of these cavities.  To understand the relationship between serous membranes and an organ, you can push your fist into an inflated balloon.  The inner balloon wall in contact with your fist (organ) represents the visceral serous membrane, and the outer part of the balloon wall represents the parietal serous membrane.  The cavity, or space, between the visceral and parietal serous membranes is normally filled with a thin, lubricating dil of serous fluid produced by the membranes. As organs rub against another organ or against the body wall, the serous fluid and smooth serous membranes reduce friction.