Question

multiple choice question
why are capillaries sometimes called the exchange vessels of the cardiovascular system?
capillaries can become either veins or arteries as needed.
capillaries exchange red blood cells for white blood cells in the liver.
blood changes direction in the capillaries and begins to flow back towards the heart.
most exchange between the blood and the tissue fluid occurs across capillary walls.
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Explanation:

To determine why capillaries are called exchange vessels, we analyze each option:

• First option: Capillaries don't transform into veins/arteries. Eliminate.
• Second option: Capillaries don't exchange red/white blood cells in the liver. Eliminate.
• Third option: Blood direction change and flow back occur in veins, not capillaries. Eliminate.
• Fourth option: Capillary walls are thin, allowing exchange of nutrients, gases, and waste between blood and tissue fluid. This matches the "exchange" role.

Answer:

D. Most exchange between the blood and the tissue fluid occurs across capillary walls. (Note: Assuming the last option is D; if options are labeled differently, adjust the identifier. Here, the correct option is the one stating "Most exchange between the blood and the tissue fluid occurs across capillary walls.")