Which of the following statements is true regarding cross sectional area and velocity of blood flow?

Question

BlackTom AI · Accepted Answer

The question asks about the relationship between cross sectional area and velocity of blood flow in the circulatory system, with a focus on capillaries.
Option 1 claims the velocity is lowest in the aorta and highest in the capillaries. This is inconsistent with physiology: the aorta has a large diameter but the velocity is actually relatively high there due to the large blood ejection into systemic circulation, while the capillaries collectively present a huge total cross-sectional area, which slows flow.
Option 2 states that cross sectional area is directly proportional to velocity in the capillaries. If cross sectional area increased and velocity increased together in capillaries, that contradicts the principle of continuity: in a network, as cross sectional area increases (sum of many tiny vessels), velocity tends to decrease to maintain flow rate, so this option is incorrect.
Option 3 claims the combined cross sectional area of the capillaries equals that of the aorta. In reality, the capillary network has a vastly larger total cross sectional area than the aorta, which is why velocity in capillaries is very slow. Therefore this statement is false.
Option 4 asserts that cross sectional area is inversely proportional to the velocity of blood flow in the capillaries. This aligns with fundamental hemodynamics: a large cumulative cross sectional area in the capillary beds reduces velocity to enable efficient exchange, whereas a small cross sectional area (like in the aorta) corresponds to higher velocity. The inverse relationship is consistent with the principle of continuity and the requirements for nutrient and gas exchange in tissues.
In summary, evaluating the statements shows that the false options misstate the relationship between area and velocity, while the true idea is that capillaries’ large total cross sectional area leads to slower velocity, i.e., an inverse relationship between cross sectional area and flow velocity in the capillaries.

Which of the following statements is true regarding cross sectional area and velocity of blood flow?单项选择题

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