Which of the following best describes a blood vessel that carries blood back to the heart?

• A. Artery
• B. Vein
• C. Capillary
• D. Lumen

Answer: (B)

Veins are the vessels that carry blood back to the heart. They return blood after it has circulated through the body, usually with lower oxygen content, and deliver it to the heart to be pumped again. Arteries instead carry blood away from the heart under higher pressure, with thicker walls to withstand that pressure. Capillaries are the tiny networks where gases, nutrients, and wastes are exchanged between blood and tissues, serving as the link between arteries and veins. The interior opening of a vessel is called the lumen, which is the space blood flows through, not a type of vessel. Veins often have valves to prevent backflow and help blood return from the extremities, especially against gravity. An exception to the general rule is the pulmonary veins, which carry oxygenated blood from the lungs to the heart.