What effect did the change in blood vessel length have on flow rate?

What effect did the change in blood vessel length have on flow rate?

• A. Flow rate increased as length increased.
• B. Flow rate remained the same regardless of length.
• C. Flow rate decreased as length increased.
• D. Flow rate fluctuated unpredictably with length.

Answer: (C)

When a fluid is driven through a vessel by a pressure difference, the resistance to flow grows with the length of the path. In laminar flow, the flow rate is proportional to the pressure difference and to factors like radius and viscosity, but inversely proportional to length. Put simply, longer vessels create more friction along their walls, so for the same driving pressure, less fluid can pass per unit time. If length doubles while the pressure difference stays the same, the flow rate drops roughly by a factor of two. That’s why the correct takeaway is that flow rate decreases as length increases. (If the body could adjust the pressure difference, it could offset this, but with a fixed driving pressure the trend is clear.)

When a fluid is driven through a vessel by a pressure difference, the resistance to flow grows with the length of the path. In laminar flow, the flow rate is proportional to the pressure difference and to factors like radius and viscosity, but inversely proportional to length. Put simply, longer vessels create more friction along their walls, so for the same driving pressure, less fluid can pass per unit time. If length doubles while the pressure difference stays the same, the flow rate drops roughly by a factor of two. That’s why the correct takeaway is that flow rate decreases as length increases. (If the body could adjust the pressure difference, it could offset this, but with a fixed driving pressure the trend is clear.)