Which epithelium lines the heart and blood vessels, and what is it called?

• A. Simple cuboidal epithelium; endothelium
• B. Stratified squamous; endothelium
• C. Simple squamous epithelium; endothelium
• D. Pseudostratified ciliated epithelium; endothelium

Answer: (C)

The heart and blood vessels are lined by a single layer of flat cells called endothelium, which is simple squamous epithelium. This thin, smooth, single-layer design provides a minimal diffusion distance and a low-friction surface for blood to flow, enabling efficient exchange and reducing resistance. The endothelium also supports vascular regulation and anticoagulant properties under normal conditions. Other epithelial types would not fit because a protective, multi-layered surface (like stratified squamous) would be too thick for the inside of vessels, while a thicker cuboidal layer wouldn’t optimize diffusion or smooth flow; pseudostratified ciliated epithelium is specialized for movement and protection in airways, not the circulatory interior.