Which cell type dominates the vascular media and is central to vascular repair and pathology?

• A. Endothelial cells
• B. Smooth muscle
• C. Fibroblasts
• D. Pericytes

Answer: (B)

The vascular media is dominated by smooth muscle cells, the contractile cells arranged in concentric layers that give arteries their muscular strength and control vessel diameter. Beyond contracting to regulate blood flow, these cells are highly plastic: after injury they can switch to a synthetic state, proliferate, migrate into the intima, and secrete extracellular matrix. This repair capacity is why they are central to remodeling and pathology, such as neointimal hyperplasia, restenosis, and atherogenesis. Endothelial cells line the intima and regulate barrier and tone but do not form the media; fibroblasts are mainly in the adventitia; pericytes stabilize capillaries, not the arterial media.