MCAT Biology Question 99: Answer and Explanation
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Question: 99
9. At any given time, there is more blood in the venous system than the arterial system. Which of the following features of veins allows for this?
- A. Relative lack of smooth muscle in the wall
- B. Presence of valves
- C. Proximity of veins to lymphatic vessels
- D. Thin endothelial lining
Correct Answer: A
Explanation:
The relative lack of smooth muscle in venous walls allows stretching to store most of the blood in the body. Valves in the veins allow for one-way flow of blood toward the heart, not stretching. Both arteries and veins are close to lymphatic vessels, which has no bearing on their relative difference in volume. Both arteries and veins have a thin endothelial lining.