Why are serous membranes double layered?

Serous membranes are double-layered to provide protection and reduce friction between organs and surrounding structures in body cavities. The outer layer, known as the parietal layer, lines the cavity walls, while the inner layer, called the visceral layer, covers the organs themselves. This arrangement allows for the smooth movement of organs, such as the lungs and heart, during physiological processes, while also creating a space filled with serous fluid that acts as a lubricant. Additionally, the double layer helps to compartmentalize the body, preventing the spread of infections and disease between organs.