Question

Which statement about the mammalian circulatory system is correct?

• A. The average diameter of arteries is greater than that of veins
• B. The order of decreasing velocity of blood flow is arteries $>$ capillaries $>$ veins
• C. The total surface area of the capillaries is considerably greater than that of all of the arteries, arterioles, venules and veins combined
• D. The electrical activity that coordinates the heating of the heart originates in the atrio-ventricular node

Answer 1

The correct option is C The total surface area of the capillaries is considerably greater than that of all of the arteries, arterioles, venules and veins combined

1. Due to narrow lumen, the average diameter of veins is greater than arteries.

2. The velocity of blood flow depends upon the cross sectional area. The order of decreasing velocity of blood flow is arteries > veins > capillaries.

3. Although the surface area of a single capillary is quite small, the number of capillaries supplied by a single arteriole is so great that the total cross-sectional area available for the flow of blood is increased. It is greater than that of all the arteries, arterioles, venules and veins combined.

4. The electrical activity that coordinates the beating of the heart originates in the Sino-atrial node.

So, the correct option is 'The total surface area of the capillaries is considerably greater than that of all of the arteries, arterioles, venules and veins combined'.