Which of the following is true of veins?

• A. Veins carry blood away from the heart.
• B. Veins have thicker walls than arteries.
• C. Veins are primarily responsible for oxygenating blood.
• D. Veins contain valves to prevent backflow of blood.

Answer: (D)

Verified step by step guidance

1. Understand the function of veins in the circulatory system: Veins are blood vessels that carry blood towards the heart. This is the opposite of arteries, which carry blood away from the heart.
2. Consider the structure of veins: Veins have thinner walls compared to arteries. This is because the blood pressure in veins is lower than in arteries, so they do not need to be as thick or muscular.
3. Evaluate the role of veins in oxygenation: Veins are not responsible for oxygenating blood. This process occurs in the lungs, where oxygen is exchanged for carbon dioxide in the blood.
4. Identify the unique feature of veins: Veins contain valves. These valves are crucial as they prevent the backflow of blood, ensuring it moves in one direction towards the heart, especially from the lower parts of the body against gravity.
5. Conclude with the correct statement: Based on the above analysis, the true statement about veins is that they contain valves to prevent backflow of blood.