Serous membranes are thin layers of tissue that line body cavities and cover organs. They produce a fluid called serous fluid, which acts as a lubricant, reducing friction between organs as they move. These membranes are found in areas such as the thoracic cavity, where they form the pleura around the lungs, and the abdominal cavity, where they create the peritoneum. There are two main layers of serous membranes: the parietal layer, which lines the cavity walls, and the visceral layer, which covers the organs themselves. This structure helps protect organs and allows for smooth movement within the body.