Which layer secretes serous fluid to keep the outside moist and prevent sticking?

• A. Mucosa
• B. Submucosa
• C. Serosa
• D. Muscular

Answer: (C)

Serosa is the outer lining of many organs within body cavities and, together with its fluid, serves as a friction-reducing lubricant. It secretes serous fluid into a tiny space between the visceral and parietal layers, so surfaces can glide smoothly and stay moist without sticking as the organs move. Mucosa, by contrast, mainly lines internal tracts and secretes mucus; submucosa is a supportive connective tissue layer, and the muscular layer provides movement. So the lubricating, moistening layer described is serosa.