Cardiovascular 101 question

[Phloston]

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A bit absurd that I'm this close to the real deal and I have to ask about this, but it is what it is and I need clarification.

If you've got increased SNS activation, you'd get increased arteriolar constriction, increased heart rate and increased venous constriction, right?

So that would mean increased mean arterial pressure and DECREASED venous pressure?

I don't have an issue with the arteries, but I'm blanking on the veins for some reason.

I would think you'd get constriction with SNS stimulation, but unlike with the arterial system, the decreased pooling in the veins would actually decrease the pressure there rather than increase it.

Can someone confirm that the venous aspect is right?

Thanks,

 

[tundri]

Increasd SNS activation, in addition to everything else you mentioned, causes venoconstriction. This in turn causes a decrease in the unstressed volume (that is normally pooled in veins) and an increase in venous return to the heart which in turn, causes an increase in cardiac output by the Frank-Starling mechanism.

Edit: ohh and yeah, that's how it causes increased MAP. However, not sure if this would increase or decrease venous pressure...hmmmm... Now I wonder. I would delete my post since I just understood where your confusion lies. In this case, I'm not sure....waiting on others to enlighten. =)

According to this link, it causes INCREASED central venous pressure. http://www.cvphysiology.com/Cardiac Function/CF007.htm

Sympathetic venoconstriction, reducing venous unstressed volume, but also decreasing venous compliance, will raise venous pressure and thus right atrial pressure, filling, and cardiac output.

Reference: http://ajpheart.physiology.org/content/295/4/H1587.full

Something minor. Still, you'll do great. Best of luck! =)

 

[CassieBagley]

During venoconstriction the diameter gets smaller, thus resistance is higher (resistance is inverse of diameter). Additionally, flow will increase under SNS stimulation due to B receptor stimulation of contractility (SV) and SA node (HR). Thus, according to the formula Resistance * Flow = Pressure, both resistance and flow are greater so the the venous pressure should definitely increase.

 

[CassieBagley]

1. Arterial constriction (a receptor) --> raises PVR --> raises diastolic BP
2. Veno constrictoin (a receptor) --> increases preload --> inc Frank-Starling --> inc SV --> inc CO
3. Inc. contractility (b1 receptor) --> inc. SV --> inc. CO & systolic BP
4. Inc HR (b1 receptor) --> inc. CO (however, in excess can impede diastolic filling time)