Endocrine: adrenals

I'm posting this on the fly because I had a small epiphany, and I want to write it down before it slips away from me.  

I was reviewing endocrine for my comprehensive exam when I suddenly realized that catecholamines are the same as epinephrine and norepinephrine.  I mean, I always knew that, but it suddenly made sense. Catecholamines work on 4 types of receptors:

A1, A2, B1, B2.

A1: located on the blood vessel, regulate (depending on their stimulation) vasoconstriction.  When we are scared, or hurt, or angry, catecholamines are released by the adrenal cortex and bind to the A1 receptors, causing the blood vessels all over the body to tighten, becoming smaller, which causes the blood pressure to raise.  

A2: when these are bound by catecholamines they cause vasodilation, however, this effect is overpowered by the intense vasoconstriction caused by the stimulation of A1 receptors.

B1: located in the heart.  When these receptors are stimulated by catecholamines, they cause the heart's pacemaker cells to become irritable.  What this means is that they fire easily, and sometimes, if the person is ill, in a messy pattern we call "dysrhythmias."  They also cause the heart to increase the strength if the contraction.  

B2: these are located in the lungs.  When these are stimulated, they cause the airways in the lungs to dilate.  They also cause the blood vessels in the lungs (and ONLY the lungs) to dilate.  

So, essentially, the same chemical causes opposite reactions in the heart and vascular system, than in the lungs.  Everything having to do with circulation will tighten up to increase blood flow to the brain, everything involving respiration will loosen and expand to promote better oxygenation.  

So when we talk about medications like Albuterol, which acts like adrenaline aka epinephrine aka a type of catecholamine, it does what it's supposed to do, which is dilate everything related to respiration.  Unfortunately (even though it's technically topical--which, in my opinion, is stupid), taking too many puffs or taking puffs too close together can cause a short-lived episode of tachycardia, because epinephrine also causes everything with the circulation system to tighten and speed up.