Blood flows most slowly in the capillaries because their
Correct answer: D. diameter exceeds that of the aorta
- A. walls are unusually thick
- B. total cross sectional area is enormous
- C. internal pressure is the highest of any vessel
- D. diameter exceeds that of the aorta
Explanation
Although each capillary is microscopic, together they present a huge total area, so the same volume of blood spreads out and slows, allowing time for exchange. Slow flow follows from area, not from wall thickness.
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