Which vessels typically contain valves to prevent backflow?

• A. Veins
• B. Arteries
• C. Capillaries
• D. Lymphatic vessels

Answer: (A)

Valves are most necessary in vessels where blood moves under low pressure and could pool or flow backward. Veins fit this pattern: they return blood to the heart from the limbs, so they rely on one-way valves (folds of the tunica intima) to prevent backflow as blood moves through the veins and as the body changes position. Arteries operate at higher pressure and rely on their elastic walls and the heart’s pumping, so they don’t contain valves. Capillaries are too small to house valves. Lymphatic vessels also have valves to keep lymph moving toward the heart, but regarding the blood vascular system, veins are the typical vessels with valves to prevent backflow.