Question about alpha 1 receptors and beta 2 receptors

[chad808]

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So I was hoping someone could help me. The sympathetic nervous system utilizes alpha and beta receptors. More specifically alpha 1 causes vasoconstriction of the blood vessels and beta 2 causes dilation or relaxation of the blood vessels. How is it that one sitmulus with both receptors located in the blood vessel do not oppose each other? Another interesting thing to note is for example, in a fight or flight situation if we are deeply cut and begin bleeding out, how does our body allow for constriction in this area to prevent the loss of blood if our sympathetic nervous system which is activated allow for constriction when our stimulus is telling our blood vessels to dilate?

I read somewhere that the majority of alpha 1 receptors are located in our skin and beta 2 receptors primarily in skeletal muscle and also depending on the concentrations of either receptor will determine its function. I don't understand how this works exactly. Could someone please help clarify!! Thank you in advance!! 😀

 

[Doctosanthewan]

In blood vessels, At low concentration of epinephrine --> Beta dominates
At high concentraion of epinephrine --> Alpha dominates

For e.g. severe stressful situation -> large concentration of epinephrine enters circulation from adrenal medulla --> alpha1 effect dominates --> vasoconstriction of vessels.
But remember at the same time, the vessel tone in muscles is primarily dependent on muscle metabolites during exercise, and not sympathetic stimulation. Sympathetic effect only exerts an effect at rest.
e.g exercise --> lactic acid & adenosine production --> vasodilation.

 

[mcloaf]

Don't cross post MCAT questions in the Step 1 forum.

 

[chad808]

Thank you for the input. Very helpful!