Destroyer 2015 Bio question #346

[zammyd]

This question states the following is true:

"The greatest resistance to blood flow is in the arterioles"

Shouldn't this be false because capillaries are smaller than arterioles and thus will have a greater resistance?

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[510586]

Arterioles can constrict to make more resistance so they are more important

 

[dentsmiley]

I was confused by this as well at first. It's basically what 510586 said - part of the arteriole's job is to actually constrict and relax to control the amount of blood that flows to the capillaries (they even have a layer of smooth muscles and sometimes 'precapillary sphincter muscles' to help them to do this). So I think the question is alluding to the actual job/role of arterioles as opposed to alluding to the diameter of capillaries vs. arterioles. Someone please correct me if I'm wrong

 

[bodmon]

From what I understand Blood pressure is most effected by the radius of blood vessels. So the more narrow a blood vessel is, the more Blood pressure there will be.

When it comes to resistance, I believe different factors come into play. Peripheral vascular resistance has to do with the friction between the capillary walls and the blood, which is highest in the arterioles.

 

[CornHusker]

The vasomotor center of the medulla controls vasoconstriction in arterials via sympathetic control. Capillaries don't have this smooth muscle to control. They are a single layer of epithelium. That's why arterials can control blood pressure whereas capillaries are constant.

 

[DAT Destroyer]

This question states the following is true:

"The greatest resistance to blood flow is in the arterioles"

Shouldn't this be false because capillaries are smaller than arterioles and thus will have a greater resistance?

The arterioles are considered the resistance vessels because they are heavily innervated by the Sympathetic adrenergic nerves. They have smooth muscle character and are therefore capable to respond to the hormonal changes by increasing or decreasing their diameter. This is how they can regulate blood pressure, by increasing or decreasing resistance to flow.
Venules, turn into capillaries, which are smaller blood vessels, but they do not have smooth muscle character, and therefore are not able to regulate blood pressure like arterioles can.
The job of the capillaries is to provide gas exchange.

Hope this helps.