In which vessels are valves found?

• A. Arteries
• B. Veins only
• C. Veins, lymph collectors, and lymph trunks
• D. Capillaries

Answer: (C)

Valves act as one-way gates to prevent backflow and keep flow moving in only one direction. In veins, they’re essential because blood must travel against gravity back toward the heart, so valves are numerous especially in the legs. Arteries don’t have valves because the heart’s pumping creates high-pressure, forceful flow that doesn’t require one-way flaps. Capillaries are too small for valves and are designed for exchange, not unidirectional transport with valves. The lymphatic system uses valves throughout its vessels—lymph collectors and larger lymph trunks—to ensure lymph travels toward the venous system and doesn’t regress. Therefore, valves are found in veins as well as in lymph collectors and lymph trunks.