In a schematic drawing of a vein, which structure is designated by letter D?

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Multiple Choice

In a schematic drawing of a vein, which structure is designated by letter D?

Valves are folds of the inner lining that form cusps inside the vein’s lumen, and they prevent backflow to help return blood to the heart against gravity. Veins have these valve-like folds because they operate under lower pressure and rely on them to maintain one-way flow, especially in the limbs. The three wall layers—tunica intima, tunica media, and tunica externa—make up the vessel wall, but they don’t create the interior flap-like structure that acts as a valve. So the labeled structure corresponds to a valve.

Valves are folds of the inner lining that form cusps inside the vein’s lumen, and they prevent backflow to help return blood to the heart against gravity. Veins have these valve-like folds because they operate under lower pressure and rely on them to maintain one-way flow, especially in the limbs. The three wall layers—tunica intima, tunica media, and tunica externa—make up the vessel wall, but they don’t create the interior flap-like structure that acts as a valve. So the labeled structure corresponds to a valve.

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