20.5b Vessel Radius

What is vessel radius?

One-half the diameter of the lumen.

How does a smaller vessel radius affect resistance?

It creates greater resistance.

Why does a smaller radius increase resistance?

Blood is closer to the vessel wall, increasing friction.

What type of flow does blood exhibit in vessels?

Laminar flow.

What is laminar flow?

Blood flows at different speeds, faster in the center and slower near the walls.

Why is flow slower near the vessel wall?

Because of friction between blood and the vessel wall.

How does the vessel wall contribute to resistance?

It creates friction that slows blood flow.

What happens to resistance as vessel radius increases?

Resistance decreases.

What happens to blood flow as vessel radius increases?

Flow increases.

Why does increasing radius decrease resistance?

Less blood contacts the vessel wall, reducing friction.

What is the relationship between flow and vessel radius?

Flow is proportional to the fourth power of the radius.

What happens when vessel radius doubles?

Blood flow increases 16 times.

Why does a small change in radius greatly affect flow?

Because flow depends on radius to the fourth power.

Which factor has the greatest impact on resistance?

Vessel radius.