What is mesothelium, and where is it found?

• A. Simple cuboidal epithelium lining ducts
• B. Pseudostratified epithelium with cilia
• C. Stratified squamous epithelium
• D. Simple squamous epithelium lining serous cavities (pleura, pericardium, and peritoneum)

Answer: (D)

Mesothelium is a single layer of flat, thin cells that forms the lining of serous membranes. This simple squamous epithelium creates a smooth, slippery surface by secreting a small amount of serous fluid, reducing friction as organs move. It specifically lines the serous cavities—such as the pleural, pericardial, and peritoneal spaces—and also covers the internal surfaces within those cavities. Other epithelial types described correspond to different locations: simple cuboidal epithelium lines ducts and tubules, pseudostratified ciliated epithelium lines much of the respiratory tract, and stratified squamous epithelium protects high-wear surfaces.