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Alpha & Beta Receptors Discussion


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#1 AnthonyM83

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Posted 10 December 2007 - 03:03 AM

Could we have a discussion on alpha-1, alpha-2, beta-1, beta-2 receptors? I have a brief limited understanding of them...but don't really understand how they're connected and integrated completely.

It seems that a receptor can do two things that usually don't go together in the same sympathetic or parasympathetic categories (like one from each category?) and only to specific areas like lungs/heart...it gets confusing.

It would specifically help, in relation to medications, neurotransmitters, physiological systems/processes (like responses to changes in BP), etc... (I'd rather not start off, b/c I'll confuse myself...) 1...2...3...go
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#2 mobey

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Posted 10 December 2007 - 05:32 AM

Anthony give us a little more info such as...
What drugs do you give that affect A&B (Epi, Salbutomol, etc) that would help guide the discussion.

Ok others may disagree but The 3 most important to BLS are A1, B1, B2,
All 3 are Adrenergic receptor sites. That is to say they are the moderator between the nervous system and the affected organ(s). So....

Beta-1 affected organ is the heart. When stimulated by adrenergic agonists such as Norepinephrine, Epinephrine (whether natural from the adrenal gland or injected by an epipen), it causes the heart to speed up (positive chronotropic), Velocity of conduction is increased (positive dromotropic), And causes an increase in contractile force ( positive inotropy). These positive affects are stimulated by the sympathetic nervous system.

If this is the kind of answer you are lookig for let us know and we will continue...But I am a slow typer to write out all the others if this is not sufficient.
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#3 AnthonyM83

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Posted 10 December 2007 - 05:54 AM

Yeah, that's the exactly the kind of thing I'm talking about. I don't have any specific meds in mine...maybe common ones used in the prehospital setting or commonly prescribed ones, so when I see a patient who has them, I have something to associate it with... I wouldn't be making decisions based on this really...it's just for the info.
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#4 mobey

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Posted 10 December 2007 - 04:56 PM

Beta 2 has a few actions, the most important to an EMT is Smooth muscle relaxation in the bronchi. Therefore when stimulated by agonists it causes the bronchi to dilate.

Alpha 1 & 2 basically cause vasoconstriction (A-1) and decrease motility in the GI system (A-2).

The parasymathetic nervous system is in charge of autoregulation at rest (feed or breed). The Parasymathetic system uses Acetycholine as a neurotransmitter.
When stimulated by pain, strong emotion, etc, the sympathetic nervous system takes over and you see these affector organs respond (fight of flight).

As far as the drugs, I will let someone else tackle them.
I have been VERY basic about this topic, however taking an EMT-B course this is probably all you really need to know till your done school and have time to read up on it more in depth.
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#5 AZCEP

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Posted 10 December 2007 - 09:07 PM

Alpha receptors are primarily affected by the presence/absence of Norepinephrine. Alpha-1 causes vasoconstriction predominantly. Alpha-2 causes the release of norepinephrine to be halted. The negative feedback mechanism that is responsible for this keeps your blood pressure from going to high when you are placed under stress.

Beta receptors are located preferrentially. Beta-1 in the cardiac tissue, and beta-2 in the smooth muscle. Beta-2 is commonly referred to as a smooth muscle relaxant, but that is only part of the effect. There is also a beta-3 receptor that is responsible for gluconeogenesis, and glycogenolysis when stimulated. This is a poorly understood mechanism presently, but the effects of any of the sympathomimetic drugs make it apparent what the beta-3 receptor is doing.

As for drugs:
Alpha-1: Norepinephrine (Levophed), and Dopamine at higher doses, epinephrine
Alpha-2: Norepinephrine
Beta-1: Dopamine at typical doses (5-10 mcg/kg/min), epinephrine, dobutamine
Beta-2: Epinephrine, Albuterol, Terbutaline
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