Identify the tissue indicated by the arrow.

Identify the tissue indicated by the arrow.

• A. Endothelium
• B. Mesothelium
• C. Simple cuboidal epithelium
• D. None of the above

Answer: (A)

Endothelium is the inner lining of blood vessels and the heart, a specialized simple squamous epithelium. The image shows a single, flattened layer of cells lining the lumen with nuclei that are elongated along the vessel axis and a thin basement membrane beneath. This thin, uniform layer is characteristic of endothelium and distinguishes it from other epithelia. Mesothelium would line serous body cavities (like peritoneum or pleura) and not the vessel lumen, and simple cuboidal epithelium would appear as cube-shaped cells with more cytoplasm, not a flat, squamous arrangement.

Endothelium is the inner lining of blood vessels and the heart, a specialized simple squamous epithelium. The image shows a single, flattened layer of cells lining the lumen with nuclei that are elongated along the vessel axis and a thin basement membrane beneath. This thin, uniform layer is characteristic of endothelium and distinguishes it from other epithelia. Mesothelium would line serous body cavities (like peritoneum or pleura) and not the vessel lumen, and simple cuboidal epithelium would appear as cube-shaped cells with more cytoplasm, not a flat, squamous arrangement.