Is "arteriolar myogenic response" an example of POSITIVE or NEGATIVE feedback?

[greenmatter]

Hello you all,

I was wondering about this: is myogenic response in arterioles an example of negative feedback, if we're talking about Blood Pressure?

While searching on the internet, I found this - and it speaks pretty much for itself:

http://www.studyinukraine.eu/wp-content/uploads/2014/05/figure_14_14_labeled.jpg

"Perfusion pressure" is supposed to be the "deltaP", so, the pressure gradient, is it right? So, I guess that a high perfusion pressure means that pressure in ARTERIES has become higher.

According to the blood flow, myogenic response is a negative feedback, since it reduces the amount of blood flowing inside arterioles.

However, by constricting arterioles, we'd basically make MAP higher, even higher than it was before. So, according to pressure, this should be a positive feedback.

Am I getting it wrong?

Many thanks for reading.

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[SBR249]

The myogenic response is purely a local regulatory mechanism and is present in different degrees depending on the tissue.

For instance, the myogenic response would be rather counterproductive for skeletal muscles and the skin because during exercise you want increased perfusion to both to satisfy increased metabolic demands in the muscle and to dissipate heat in the skin. Myogenic clamping due to increased perfusion pressures in both would inhibit both functions.

However, myogenic response is absolutely necessary in the kidneys and the brain because they both have low tolerance for fluctuations in blood pressure - the kidneys require consistent BP for filtration and the brain requires a consistent supply of oxygen and is very delicate.

On top of all this, myogenic responses do not all have the same sensitivity, meaning that one tissue may respond under a certain condition while another tissue may not.

Having established that, myogenic response is a negative feedback mechanism because it acts locally to moderate any excursions in perfusion pressure from the normal level. It would be incorrect to talk of its systemic effects because it is not present in all tissues to the same degree and effect.

tl;dr: you can only talk about local effects of myogenic response because it does not act systemically.

 

[greenmatter]

Very well. So, I only have to consider what's happening to the arteriole itself - and not what's happening in arteries/capillaries. Therefore, it's a negative feedback about blood flow arriving to that arteriole.

Many thanks for your answer! 🙂