Inner Layer of Blood Vessels

Steps:

• Identify the layers of blood vessels: tunica intima (inner), tunica media (middle), tunica externa (outer).
• Focus on veins and capillaries: both have a thin tunica intima as the innermost layer.
• Recall tunica intima composition: lined by a single layer of flat cells called endothelium.
• Confirm endothelium lines all blood vessels, including veins and capillaries, for smooth blood flow.

Why C is correct:

• Endothelium is the simple squamous epithelial lining of the tunica intima, providing a non-stick surface for blood.

Why the others are wrong:

• A. Collagen fibres form the structural support in the tunica externa, not the inner layer.
• B. Elastic fibres are concentrated in the tunica media of arteries for stretch and recoil.
• D. Smooth muscle cells are in the tunica media to regulate vessel diameter.

Final answer: C