Arteriole Vasoconstriction

[plzNOCarribbean]

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Hey Everyone,
I did a search on this and found several posts, but none of them addressed this specific question so I am asking it now before my exam because i would really like some clarification from you experts.

In the notes from MCAT rev, it says that both arterioles and veins have the ability to vasoconstrict, while capillaries do not. It mentions that there are two types of arteries, Elastic and Muscular (distributing arteries). It notes that elastic arteries are not active in vasoconstriction, while muscular arteries, there is some vasoconstriction but that generally, "The arteriole is the most important site for vasoconstriction. Although other vessels are capable of vasoconstriction, you should always think of the arteriole when you see vasoconstriction."

is this correct? it then goes on to say:
Venule- no vasoconstrction
Veins: Vasconstriction can occur in the vein

However, on one of the AAMC tests (#9) the question asks

one characteristic common to capillaries, veins, and arteries:
a) the presence of a layer of endothelial cells
b)the presence of numerous valves that prevent the backflow of blood
c) the ability to actively dilate or constrict in regulating blood flow.

A was the right answer. And while i realize thats prob the best choice since capillaries neither dilate or constrict, the answer to the solutions says that "C is incorrect because only certain types of arteries dilate or constrict to regulate blood flow"; However, it never mentions that VIENS/VENULES do this

so my question is, do veins and venules participate in vasoconstriction? or should i just associate vasoconstriction with arterioles? I know that was long but i wanna know this. It was not addressed in any other posts.

 

[Zedor]

Hey Everyone,
I did a search on this and found several posts, but none of them addressed this specific question so I am asking it now before my exam because i would really like some clarification from you experts.

In the notes from MCAT rev, it says that both arterioles and veins have the ability to vasoconstrict, while capillaries do not. It mentions that there are two types of arteries, Elastic and Muscular (distributing arteries). It notes that elastic arteries are not active in vasoconstriction, while muscular arteries, there is some vasoconstriction but that generally, "The arteriole is the most important site for vasoconstriction. Although other vessels are capable of vasoconstriction, you should always think of the arteriole when you see vasoconstriction."

is this correct? it then goes on to say:
Venule- no vasoconstrction
Veins: Vasconstriction can occur in the vein

However, on one of the AAMC tests (#9) the question asks

one characteristic common to capillaries, veins, and arteries:
a) the presence of a layer of endothelial cells
b)the presence of numerous valves that prevent the backflow of blood
c) the ability to actively dilate or constrict in regulating blood flow.

A was the right answer. And while i realize thats prob the best choice since capillaries neither dilate or constrict, the answer to the solutions says that "C is incorrect because only certain types of arteries dilate or constrict to regulate blood flow"; However, it never mentions that VIENS/VENULES do this

so my question is, do veins and venules participate in vasoconstriction? or should i just associate vasoconstriction with arterioles? I know that was long but i wanna know this. It was not addressed in any other posts.

You should limit it to arterioles. Muscular veins can "venoconstrict", which essentially increases venous return, as it is predominantly affecting the compliance. When you think of vasoconstriction, it usually mediates an increase in resistance--whether locally to divert blood, or large scale to increase TPR.

 

[MightyMoose]

I always think of veins as collecting ducts. They don't really regulate blood flow in the typical sense. They usually return blood via muscular contraction that pushes blood beyond valves, which prevent blood backflow, but you really don't get vasoconstriction in the veins, thus limited to no blood pressure that is not created by gravity. Veins are more like a flaccid noodle (to give you some imagery).

 

[plzNOCarribbean]

ok! Thank you guys for clarifying.

Also, since you guys mentioned that the arterioles are where the majority of vasoconstriction occurs, is it correct to say that pressure is greatest in the:

Veins<Venules<Capillaries<Arterioles<Arteries

or do capillaries have the lowest pressure?

 

[Zedor]

ok! Thank you guys for clarifying.

Also, since you guys mentioned that the arterioles are where the majority of vasoconstriction occurs, is it correct to say that pressure is greatest in the:

Veins<Venules<Capillaries<Arterioles<Arteries

or do capillaries have the lowest pressure?

Pressure is highest in the arteries, and drops in the reverse order of what you listed. Think of it as Kirchkoff's rules, but instead of a voltage drop, we have a pressure drop as we continue through the circulation. Pressure=Flow*Resistance (Voltage=Current*Resistance). Because the arterioles offer the greatest resistance, they will provide the greatest pressure drop. Because the venous system is last, the pressure is smallest there. Also, because the veins offer low resistance, you don't need a large pressure gradient to return blood to the heart--as compared to getting blood from the aorta through the capillaries, and into the venous side.

 

[Zedor]

Btw, nice avatar..Atul is the man hah.