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Arteriolar Radius and Blood Flow

What determines the rate of flow in a blood vessel? The movement of a fluid through a tube is determined by several factors. One is the force applied to the fluid. In the circulatory system muscular contractions of the heart supply the force. The more rapidly the heart beats, the greater the force. The other major factor that determines the rate of flow is the radius of the blood vessel(s) the blood moves through. The arteries divide as they move away from the heart. The rate of flow decreases for two reasons. One reason is that the total volume increases. The other is that the radius of each individual artery decreases after each division. The total surface area of the arteries increases relative to the volume. Therefore there is more friction acting on the blood and reducing the rate of flow.

View the animation below, then complete the quiz to test your knowledge of the concept.






1The blood flow to the body organs...
A)is regulated exclusively by the heart stroke volume.
B)is regulated exclusively by the heart rate.
C)remains constant.
D)is directly proportional to the resistance of the arterioles leading to them.
E)is inversely proportional to the resistance of the arterioles leading to them.



2Vasodilation...
A)decreases blood flow and increases blood pressure.
B)increases blood flow and decreases blood pressure.
C)decreases both blood flow and blood pressure.
D)increases both blood flow and blood pressure.
E)has a minimal effect on blood flow and blood pressure.



3Vasoconstriction...
A)decreases blood flow and increases blood pressure.
B)increases blood flow and decreases blood pressure.
C)decreases both blood flow and blood pressure.
D)increases both blood flow and blood pressure.
E)has a minimal effect on blood flow and blood pressure.



4Blood pressure is directly proportional to vessel resistance.
A)True
B)False



5Blood flow is affected by both blood pressure and vessel resistance.
A)True
B)False







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