low pressure baroreceptors?

[alyngerj]

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Can someone explain to me how pulmonary artery and atrial low pressure receptors work? Guyton and Hall seems to gloss over it a bit. Are they activated only when there is low volume, stimulating vasomotor center to constrict? Or is it that they are normally activated, inhibiting vasoconstriction and vasopressin release unless low pressure deactivates them? Thanks!

 

[MedStudentWanna]

I thought baroreceptors responded to blood pressure. If there's low blood pressure, the baroreceptor's firing rate would decrease, encouraging vasoconstriction and vasopressin, not inhibiting it.

I could be wrong though.

 

[shadowfox87]

I'm assuming you're talking about the Bainbridge reflex, which has low pressure receptors. Yes, I was confused about this once too. The tricky part is that these low pressure receptors are activated when CVP is HIGH (not low). So yea..it seems contradictory and you might ask why are they called "low pressure receptors" then? Basically, low pressure receptors detect a deviation FROM low pressure.

In Bainbridge reflex, inc. in CVP->atrial stretch->activation of LP receptors->signal medullary centers->dec. parasympathetic tone. This is in contrast to baroreceptor reflex, in which when activated by increased stretch, sends more inhibitory signal to sympathetic-->inc. parasympathetic tone. So yea both reflex are continually activated, but each to a certain degree based on stretch.

Also, make sure you don't call it Brainbridge reflex b/c it has nothing to do with cerebral perfusion.

So when there's low volume->dec. stretch->dec. pressure->more vasopressin-->blood volume inc.

 

[mddoc1]

They respond to increased blood volume and work to control arterial pressure by causing vasodilation and bradycardia.

 

[mddoc1]

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