As blood in the systemic circuit flows from the heart to the capillaries, why is the velocity of blood flow the lowest in capillaries?
A.The capillaries have one-way valves that slow the passage of blood through them.
B.The total surface area of the capillaries is larger that of the blood vessels leading to the capillaries.
C.The systemic capillaries are supplied by the left ventricle, which has a lower cardiac output than the right ventricle.
D.The diastolic blood pressure is too low to deliver blood to the capillaries at a high flow rate.
E.The capillary walls are not thin enough to allow oxygen to exchange with the cells.
Answer Key: B