Step I cardiac output question

[Turtlez]

Why does an increase in cardiac output lead to a decrease in sympathetic activity and reduced vascular resistance? Is this effect mediated by baroreceptors in the aortic arch and carotid sinuses? Please explain the mechanism in detail if you can. Thank you so much!

 

[MudPhud20XX]

Yes I think so. It is associated with the autonomic feedback loop.

Blood pressure is the product of the TPR and CO as you know right?
And both branches of the ANS are involved in the autonomic control of blood pressure via feedback mechanisms.

I looked at Kaplan pharm and it says:

"Changes in mean blood pressure are detected by varoreceptors, which relay information tot he cardiovascular centers in the brainstem controlling PANS and SANS outflow. For example, an increase in mean blood pressure elicits baroreceptor discharge, resulting in increased PANS activity, leading to bradycardia and decreased SANS activity, which leads, in turn, to decreased heart rate, force of contraction, and vasoconstriciton. The resulting decreases in cardiac output and total peripheral resistance contribute to restoration of mean blood pressure toward normal level."

So going back to your question:

Increased CO --> Increases blood pressure (=mean arterial pressure) --> elecits baroreceptro discharge --> increased PANS activity and decreased SANS

Does this make sense?

Please feel free to correct me or add any further explanation.
Thanks.

 

[Juan Solo]

Yup.

Increase in cardiac output = increase in MAP = detection via baroreceptors in aortic and carotid bodies = decrease sympathetic outflow to vascular smooth muscle = dilation (decrease in vascular resistance) = readjustment or lowering of MAP back to normal ranges.