Which vessel carries blood back toward the heart from the body's tissues?

• A. Arteries
• B. Veins
• C. Capillaries
• D. Venules

Answer: (B)

Blood returns to the heart through veins. After blood delivers oxygen and nutrients to tissues, it collects in small vessels called venules and then drains into larger veins that carry it back toward the heart, completing the systemic circulation. Veins are designed for returning blood: they operate at lower pressure, have thinner walls and larger lumens, and often include valves to prevent backflow as the blood moves toward the heart, helped by muscle contractions and breathing. In contrast, arteries carry blood away from the heart, and capillaries are the tiny exchange vessels between them. (A quick note: in the systemic circulation, veins usually carry deoxygenated blood; the exception is the pulmonary veins, which return oxygenated blood from the lungs to the heart.)