Nobody else is answering your question so I might as well take a stab at it. I wish your questions were a little more specific. It would also be nice to know whether this is a ALS or BLS question.
Nervous system is composed of CNS which is brain and spinal cord and PNS which is everything else.
The Autonomic Nervous System (ANS) is a component of the PNS and is the system of regulation. The ANS has 2 parts, the parasympathetic system and the sympathetic system.
Parasympathetic System (cholinergic system) is controlled through vagus nerve and its primary mediator is acetylcholine. This system slows down everything except the GI tract (increases peristalsis). It slows heart rate, respiration rate, and decreases BP.
Sympathetic system (adrenergic system) does the opposite and increases everything except peristalsis (thats why upset people have upset stomachs). Another words, it increases HR, RR, and BP. Its primary mediator is Norepinephrine, epinephrine. This system is stimulated through the Alpha and Beta receptors. Alpha receptors cause bronchoconstriction and vasoconstriction. Beta receptors cause increase HR, bronchodilation and vasodilation. Ex. epinephrine stimulates both alpha and beta receptors and that's why it does what it does.
Shock is widespread inadequate tissue perfusion. It is caused by low blood volume, mechanical heart problems (the hearts not pumping good enough because of tension pneumothroax, myocardial contusion, etc.), or relative hypovolemia (neurogenic shock) where nervous system relaxes muscle tension on veins and suddenly there is not enough blood to maintain adequate BP.
When someone goes into shock, the ANS jumps into action when the sympathetic system releases epi which as we now know increases vasoconstriction, increases HR, shunts blood to vital organs (brain and heart) and hopefully increases BP.
This is only the beginning. There have been books written on shock. Hopefully this will give you a basic understanding.
