Major Vein Structure: Thin Media, Thick Adventitia

Steps:

• Recall vein histology: three layers—tunica intima (endothelium), thin tunica media (smooth muscle), thick tunica adventitia (connective tissue).
• Compare to arteries: veins have larger lumen, thinner media for low pressure.
• Identify diagram features: look for prominent outer layer, minimal middle muscle, no valves (unless specified).
• Match to options: select diagram showing thin middle layer and thick outer layer.

Why D is correct:

• Diagram D depicts thin tunica media and thick tunica adventitia, matching vein definition for flexibility and low-pressure return.

Why the others are wrong:

• A shows thick tunica media, typical of elastic artery.
• B illustrates single endothelial layer, characteristic of capillary.
• C features prominent smooth muscle in media, resembling muscular artery.

Final answer: D