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If the radius of an arteriole increases from 2 to 3 mm how does this affect resistance and blood flow?
Wiki User
∙ 16y ago
Intuitively, it's easy to think of blood flow through the arteries in the same way that you think of the flow of water through pipes. Change the radius of the pipe, and you change how fast water flows to them. Likewise, if you change the radius of an arteriole, you change the rate that blood flows through it.
The underlying reason behind these observations is the same. Flow (Q) is determined by a pressure gradient (ΔP) and the resistance to flow (R):
Q = ΔP / R
If you increase resistance, you decrease flow; likewise, decrease resistance and you increase flow. But what determines resistance? Poiseuille's law tells us that resistance (R) is inversely proportional to the fourth power of radius (r).
So let's say we take a normal blood vessel and measure the resistance; let's call that resistance R1. Now if we double the vessel radius, what happens to the resistance? Poiseuille's law (see link to left) tells us that if we double the radius, our resistance goes down by a factor of 16. So R2 is one-sixteenth of R1.
How does this affect blood flow? For that we go to our original equation that related flow, pressure gradient, and resistance. From that you can see that flow is inversely proportional to resistance. So if you halve resistance, then you double flow; likewise, if you take our example and reduce resistance to a factor of one-sixteenth, then flow increases by a factor of 16.
The same principles and steps can be used to figure out what happens when you change the radius of an arteriole from 2 mm to 3 mm. Only this time you're not increasing radius by a factor of 2; you're increasing it by a factor of 3 / 2, or 1.5.
Wiki User
∙ 16y ago
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