Worrier's Guide to Adrenalin

[joelhall]

Just wrote this up out of boredom, hope it's helpful to some people:

The Worrier’s Very Brief Guide to Adrenalin (Epinephrine)

J. G. Hall

Introduction
There will be some technical terms used in this article, however these will all be explained so the reader can get a better understanding or the endocrine (hormonal) and neurological effects of this hormone.
Noradrenalin (or norepinephrine in the USA) is classed as a neurotransmitter. This is it is released at the end of one nerve and binds to the end of another so that nerves can communicate with each other and send signals from the CNS to tissues. Noradrenalin also is released at the end of nerves to bind to certain tissue cells. This is how the nerves signal the body to do work.
The autonomic nervous system (ANS) is an involuntary system, divided into three parts: sympathetic, parasympathetic and enteric. The sympathetic nervous system has the job of preparing the body for activity, and is responsible for the ‘fight or flight’ response. By contrast the parasympathetic nervous system has the job of restoring the body to rest and conserving energy. The enteric nervous system is located in the gastrointestinal system.
The way these nerves communicate, as noted above, is by the use of neurotransmitters, at a junction called a synapse. This is essentially simply a gap filled with fluid. The nerve which ends at the synapse is called the pre-synaptic neuron, while that which begins at the junction is called, rather obviously, the post-synaptic neuron. When a signal reaches the end of the pre-synaptic neuron, a neurotransmitter is released, diffuses through the fluid, and binds to the post-synaptic neuron, which then stimulates this fibre to carry a signal. Really they can be thought of as relays along a circuit. There are various types of these neurons and the receptors on post-synaptic neurons, however we will be only concerned with those related to noradrenalin and adrenalin. This are known as adrenergic neurons (which release noradrenalin) and adrenoreceptors (which receive noradrenalin).
Noradrenalin is what is known as an excitory neurotransmitter. This does not mean of course it makes you excited, but describes its effects on the receptor it binds to. Excitory neurotransmitters cause the cell to do something, whilst inhibitory neurotransmitters cause a cell to not do something. Although it probably doesn’t need say, these exist in the sympathetic nervous system, the one which prepares our bodies.
First let us look at the receptors:

The Adrenoreceptors

There are four types of adrenoreceptor located in the sympathetic nervous system: α1 α2 β1 β2. Anyone who has heard of β-blockers, will probably be familiar with their mechanism of action – they block the β-adrenoreceptors so that noradrenalin cannot bind to them, and so the excitory message is not given to the post-synaptic neuron. Before moving on to the chemicals, let us see where each of these adrenoreceptors is, and what some example of the effect stimulating them has:
α1-receptors:
- smooth muscle of blood vessels of the skin – constriction
- smooth muscle of blood vessels in skeletal muscle - constriction
- smooth muscle sphincters of the gastrointestinal tract – contraction
- sphincter of the bladder – contraction
- iris muscles of the eye (surrounding the pupil) – mydriasis (pupil dilation)
- stress sweat glands – increases secretion
- pilomotor muscles (attached to hairs in the skin) – contraction (i.e. ‘goosebumps’)
- liver – release of glucose into the blood
α2-receptors:
- walls of the gastrointestinal tract – relaxation
- stress sweat glands (as above)
- pilomotor muscles (as above)
- liver (as above)
β1-receptors:
- SA node – increases heart rate
- AV node – increases heart cell conduction
- Cardiac muscle contractility – increases, beats more powerfully
- Saliva, gastric acid and pancreatic secretion – all increase
- Ciliary muscle of the eye – increases long-distance vision by contraction
- Fat cells – lipolysis (breaks down fat for energy)
- Renin secretion from the kidney increases
β2-receptors:
- Dilation of the bronchioles in the lungs
- Dilation of the coronary arteries
- Relaxes the walls of the gastrointestinal tract
- Relaxes the walls of the bladder
- Ciliary muscles (as above)
- Liver, releases glucose into the blood
- Dilation of the skeletal muscle blood vessels
β3-receptors have been left out of this discussion.
As you can see a fair few effects, which many of us recognise. But what happens during a panic attack, and why all that stuff about noradrenalin, when we all know it’s adrenalin which causes them. Allow me to explain the chemicals themselves:

The Catecholamines

The catecholamines are a group of related chemicals including adrenalin and noradrenalin. In our usual day to day lives, noradrenalin keeps us alive – as can be seen from the above section it has important effects which keep our hearts beating, our blood sugar regulated, makes sure we don’t wet ourselves (too often), and keeps our secretions…. Secreting!
However, other than the usual neurons, there is an exceptional part of the sympathetic nervous system which is really a gland – the adrenal medulla. It is this gland which secretes adrenalin into the circulation – which means it ends up pretty much everywhere, and wherever there is a receptor it binds.
Now, ordinarily, this isn’t a problem. The sympathetic nervous system works all day long, as signals travel along neurons from the CNS directing what needs to be produced to do what. On the treadmill? Up goes the stimulation from the brain to produce more noradrenalin to make the heart pump faster.
We are all familiar with this symptoms during a panic attack. But what is so different about it from our normal day-to-day life? Stimulation. The stimulation of the sympathetic nervous system rapidly increases. And it is not only adrenalin which is increased, but noradrenalin from the neurons mentioned before, AND from the adrenal medulla into circulation (approximately 20% noradrenalin, 80% adrenalin is released).
So what does this all mean? How do we explain the symptoms? Here is a list of those symptoms almost always present when the sympathetic nervous system decides to have fun with us. These things are not just restricted to panic attacks either, but anything which increases the stimulation of the sympathetic nervous system:
Tachycardia (rapid heart rate)
Muscle tension/trembling/pain/poor coordination
Increased blood pressure
Increased respiratory rate
Dilation of the pupils and blurred short distance vision/tunnel vision
Increase in body temperature
Sweating/Cold sweat (as the thermoregulatory sweat glands are not stimulated by catecholamines, only the stress sweat glands)
Dizziness
Sleep difficulties
Sexual difficulties
Headaches and chest pains
Fatigue
Gastric upsets

Now this list isn’t exhaustive of every possible symptom, only those which will affect most people, most of the time, (for example for some people poor hearing or loss of hearing temporarily can happen). But these effects are the root cause of practically every other physical symptoms occurring in anxiety and panic.
Ah yes, general anxiety. What is going on there, you don’t have a panic attack but you still feel funny. Quite simply this: These chemicals are not simply switched on or off, but levels fluctuate. You will not produce the same amounts al day every day. Nobody does, even those without anxiety. It’s a sliding scale and goes up and down constantly, working with the parasympathetic nervous system to regulate everything. So you may experience less severe symptoms for an hour, 2 hours, 24 hours, a week… simply because there is more stimulation than necessary. The answer hear is fairly obvious – learn to relax more often and find ways to cope with stress, whether it be painting, yoga, lying on the beach with bikini-clad ladies serving you cocktails, or even a quick nap in the afternoon.
And that parasympathetic nervous system – that’s the one which calms you down

[Ccat]

wow- thank you ! xxx

[Jen20]

Amazing!