Adrenaline

Ever had an adrenaline rush? Ever had stage fright or been on a roller coaster? When your body is about to have to do something extreme, your brain turns on the “fight or flight” response. Your brain uses hormones to talk to your body. Hormones can do different things to different kinds of cells. In an emergency adrenaline, the “fight or flight” hormone, floods the blood stream which affects different parts of your body in different ways. Adrenaline acts on three different systems: blood vessels, blood chemistry, and the brain.


Blood vessels (blood goes to muscles, not to gut)
You’ll need your arms and legs in top shape if you’re going to run or fight. Your body delivers more oxygen to these muscles, called the skeletal muscles, by “dilating” the blood vessels, opening them up to let more blood in. Since you won’t really need to digest food, the blood vessels in your gut, called smooth muscles, “constrict” or become smaller.

The hormone can affect different kinds of blood vessels differently because of the different kinds of adrenaline (adrenergic) receptors these cells have. The blood vessels in skeletal muscles have β2 receptors. When adrenaline binds these receptors the blood vessels respond by dilating. The blood vessels in smooth muscles have α receptors and they respond to adrenaline by constricting.

Blood chemistry (blood sugar, fat break down)
Adrenaline gives you a rush of energy because it raises blood sugar. Muscles burn sugar, in the form of glucose, to produce energy.

Most of the time, the liver puts glucose into molecules of glycogen so it can send glycogen to muscle cells. Adrenaline tells the liver that you need sugar fast. Your liver stops making glycogen and starts breaking it down to glucose which it releases into the blood stream. Muscles react to adrenaline by using sugar from the blood stream and by breaking glycogen down to glucose.

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Glycogen
Say you have three 12 packs of coke in boxes. If you open all those boxes and put them in your fridge it’ll be easy for you to grab a coke and drink it. It’ll be harder to give your friend 12 cokes to take to a party. If you keep the coke in the boxes you can just hand your friend a box.
The liver stores units of sugar, glucose, in the form of glycogen. It takes 5 units of glucose to make a molecule of glycogen. For the liver cell, it’s like having a 12 pack of coke instead of having to deal with 12 cans. It saves on shipping and handling.
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The liver uses some of the sugar it gets to make fat. The fat is shipped to fat cells called adipocytes where it’s stored. Adrenaline tells the liver and fat cells to break fat down so it can be used as fuel by muscles. Fat cells usually hang out next to muscle cells so that the fuel doesn’t have far to go.


Brain (Neurotransmitter)
Hormones have to travel through the bloodstream to reach cells and send them messages. Neurotransmitters just jump between brain cells called neurons.

A part of the brain called the medulla oblongata controls your heart beat and breathing. Adrenaline tells this part of the brain to make the heart beat faster and stronger, which raises blood pressure. Adrenaline makes breathing faster and shallower and dilates (expands) the lungs so they can get more oxygen. More oxygen in the blood and higher blood pressure mean that muscles get more oxygen and can work harder.

Adrenaline also alters perception. Though pupils dilate, people often have tunnel vision during a stressful situation, sounds can seem muffled and some people even report a loss of color vision as the mind becomes more focused on whatever situation is at hand. Often our memory of an important event is somewhat distorted. Sometimes it feels like something happened “in a blur” or very quickly while other moments seem as if they lasted much longer than they did.


extra info:
Adrenaline is known as epinephrine in the United States due to copyright laws. Adrenaline comes in two major forms: adrenaline and noradrenaline, known as epinephrine and norepinephrine in the US. Epinephrine activates all adrenergic receptors, norepinephrine activates all but the β2 receptors. Norepinephrine has different actions on different cell types but I was unable to determine exactly what those differences are.


please tell me more
If anybody knows the differences between epinephrine and norepinephrine, please tell me! I’m also curious about the effects of epinephrine on the brain, a subject I hope to write more about later.