Which statement about increasing vessel length is true?

Which statement about increasing vessel length is true?

• A. Decreases resistance
• B. Decreases flow
• C. Has no effect on resistance
• D. Increases resistance, same as decreasing radius

Answer: (D)

Increasing vessel length raises resistance because resistance grows with length while keeping viscosity and radius constant. In Poiseuille flow, R is proportional to L divided by r^4, so doubling the length doubles the resistance. With a fixed pressure difference, higher resistance means lower flow. This change mirrors what happens when radius decreases, since resistance also rises as radius shrinks (R ∝ 1/r^4). So increasing length increases resistance, just as decreasing radius does. The other statements don’t match this direct relationship: length does not decrease resistance, it does not have no effect, and while flow can drop with longer length at constant pressure, the fundamental effect is the rise in resistance.

Increasing vessel length raises resistance because resistance grows with length while keeping viscosity and radius constant. In Poiseuille flow, R is proportional to L divided by r^4, so doubling the length doubles the resistance. With a fixed pressure difference, higher resistance means lower flow. This change mirrors what happens when radius decreases, since resistance also rises as radius shrinks (R ∝ 1/r^4). So increasing length increases resistance, just as decreasing radius does. The other statements don’t match this direct relationship: length does not decrease resistance, it does not have no effect, and while flow can drop with longer length at constant pressure, the fundamental effect is the rise in resistance.