Question

question 6
the velocity of blood flow lowest in capillaries because _.
a the total cross - sectional area is greater in the capillaries than in any other part of the circulatory system
b the capillaries have internal valves that slow the flow of blood
c the diastolic blood pressure is too low to deliver blood to the capillaries at a high flow rate
d the systemic capillaries are supplied by the left ventricle, which has a lower cardiac output than the right ventricle

Explanation:

According to the principle of blood flow, the velocity of blood flow is inversely proportional to the total cross - sectional area of the blood vessels. Capillaries have an extremely large total cross - sectional area compared to other parts of the circulatory system. This large area results in a lower velocity of blood flow, which is beneficial for the exchange of substances between blood and tissues.

• Option B: Capillaries do not have internal valves. Valves are mainly found in veins.
• Option C: Diastolic blood pressure is not the main reason for the low velocity of blood flow in capillaries.
• Option D: The left ventricle has a higher cardiac output than the right ventricle as it supplies blood to the whole body (systemic circulation), while the right ventricle only supplies blood to the lungs (pulmonary circulation).

Answer:

A. the total cross-sectional area is greater in the capillaries than in any other part of the circulatory system