Which of the following blood vessels have lowest blood velocity with correct reason for low blood velocity?
Correct answer: B. Capillaries: due to highest overall cross-sectional area
- A. Arteries: Due to thick walls
- B. Capillaries: due to highest overall cross-sectional area
- C. Veins: due to blood flow against the gravity
- D. Capillaries: Due to two-way blood flow in capillaries
Explanation
Although each capillary is tiny, there are so many in parallel that their combined cross sectional area is far greater than that of the aorta, and since the same volume must pass every second, the velocity falls to about a millimetre per second. That slow flow is exactly what exchange requires, giving time for diffusion. The fourth option names the right vessel but an invented reason, since capillary flow is one way.
This question appeared on the UHS MDCAT 2025 paper, which you can sit online with every answer explained.
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About Blood Vessels
Blood vessels include arteries, arterioles, capillaries, venules and veins, whose wall thickness, elasticity, lumen size and valves suit their roles in circulation. Questions compare pressure and blood flow in each vessel and distinguish pulmonary vessels, which carry blood to and from the lungs, from systemic vessels.
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