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  • Ethanol: this molecule, made of little more than a few carbon atoms,

  • is responsible for drunkenness.

  • Often simply referred to as alcohol,

  • ethanol is the active ingredient in alcoholic beverages.

  • Its simplicity helps it sneak across membranes

  • and nestle into a many different nooks,

  • producing a wide range of effects compared to other, clunkier molecules.

  • So how exactly does it cause drunkenness,

  • and why does it have dramatically different effects on different people?

  • To answer these questions,

  • we'll need to follow alcohol on its journey through the body.

  • Alcohol lands in the stomach and is absorbed into the blood

  • through the digestive tract, especially the small intestine.

  • The contents of the stomach impact alcohol's ability

  • to get into the blood because after eating, the pyloric sphincter,

  • which separates the stomach from the small intestine, closes.

  • So the level of alcohol that reaches the blood after a big meal

  • might only be a quarter that from the same drink on an empty stomach.

  • From the blood, alcohol goes to the organs,

  • especially those that get the most blood flow:

  • the liver and the brain.

  • It hits the liver first, and enzymes in the liver

  • break down the alcohol molecule in two steps.

  • First, an enzyme called ADH turns alcohol into acetaldehyde, which is toxic.

  • Then, an enzyme called ALDH converts the toxic acetaldehyde to non-toxic acetate.

  • As the blood circulates, the liver eliminates alcohol continuously

  • but this first pass of elimination determines how much alcohol

  • reaches the brain and other organs.

  • Brain sensitivity is responsible for the emotional, cognitive,

  • and behavioral effects of alcoholotherwise known as drunkenness.

  • Alcohol turns up the brain's primary brake, the neurotransmitter GABA,

  • and turns down its primary gas, the neurotransmitter glutamate.

  • This makes neurons much less communicative,

  • and users feel relaxed at moderate doses, fall asleep at higher doses,

  • and can impede the brain activity necessary for survival at toxic doses.

  • Alcohol also stimulates a small group of neurons

  • that extends from the midbrain to the nucleus accumbens,

  • a region important for motivation.

  • Like all addictive drugs,

  • it prompts a squirt of dopamine in the nucleus accumbens

  • which gives users a surge of pleasure.

  • Alcohol also causes some neurons to synthesize and release endorphins.

  • Endorphins help us to calm down in response to stress or danger.

  • Elevated levels of endorphins contribute to the euphoria

  • and relaxation associated with alcohol consumption.

  • Finally,

  • as the liver's breakdown of alcohol outpaces the brain's absorption,

  • drunkenness fades away.

  • Individual differences at any point in this journey

  • can cause people to act more or less drunk.

  • For example, a man and a woman who weigh the same and drink the same amount

  • during an identical meal will still have different blood alcohol concentrations,

  • or BACs.

  • This is because women tend to have less blood

  • women generally have a higher percentage of fat,

  • which requires less blood than muscle.

  • A smaller blood volume, carrying the same amount of alcohol,

  • means the concentration will be higher for women.

  • Genetic differences in the liver's alcohol processing enzymes also influence BAC.

  • And regular drinking can increase production of these enzymes,

  • contributing to tolerance.

  • On the other hand, those who drink excessively for a long time

  • may develop liver damage, which has the opposite effect.

  • Meanwhile, genetic differences in dopamine, GABA,

  • and endorphin transmission may contribute to risk

  • for developing an alcohol use disorder.

  • Those with naturally low endorphin or dopamine levels may self-medicate

  • through drinking.

  • Some people have a higher risk for excessive drinking

  • due to a sensitive endorphin response that increases the pleasurable effects

  • of alcohol.

  • Others have a variation in GABA transmission

  • that makes them especially sensitive to the sedative effects of alcohol,

  • which decreases their risk of developing disordered drinking.

  • Meanwhile, the brain adapts to chronic alcohol consumption by reducing GABA,

  • dopamine, and endorphin transmission, and enhancing glutamate activity.

  • This means regular drinkers tend to be anxious, have trouble sleeping,

  • and experience less pleasure.

  • These structural and functional changes can lead to disordered use

  • when drinking feels normal, but not drinking is uncomfortable,

  • establishing a vicious cycle.

  • So both genetics and previous experience impact how a person experiences alcohol

  • which means that some people are more prone

  • to certain patterns of drinking than others,

  • and a history of consumption leads to neural and behavioral changes.

Ethanol: this molecule, made of little more than a few carbon atoms,

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B2 US TED-Ed alcohol liver blood drinking dopamine

How does alcohol make you drunk? - Judy Grisel

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    Annie Huang posted on 2020/04/11
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