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Ethanol: this molecule, made of little more than a few carbon atoms, is responsible for drunkenness.
乙醇：其分子是由碳原子组成，能够让人产生醉意。
Often simply referred to as alcohol, ethanol is the active ingredient in alcoholic beverages.
乙醇通常被简称为酒精，是含酒精饮料中的活性成分。
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.
简单的分子结构使它能透过细胞膜，并停留在许多不同位置，从而比其他较重的分子产生更多的影响。
So how exactly does it cause drunkenness, and why does it have dramatically different effects on different people?
那么乙醇是怎样让人产生醉意的，为什么它对不同人的影响会有天壤之别？
To answer these questions, we'll need to follow alcohol on its journey through the body.
要回答这些问题，我们就要跟着酒精去看看它在人体内的旅程。
Alcohol lands in the stomach and is absorbed into the blood through the digestive tract, especially the small intestine.
酒精首先进入胃部，通过消化道，尤其是小肠，被血液吸收。
The contents of the stomach impact alcohol's ability to get into the blood because after eating,
胃里的东西会影响酒精进入血液的能力，因为进食之后，
the pyloric sphincter, which separates the stomach from the small intestine, closes.
幽门括约肌闭合，而幽门括约肌是分隔胃部和小肠的部分。
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.
所以在一顿大餐过后，酒精进入血液的能力可能只有空腹时的四分之一。
From the blood, alcohol goes to the organs, especially those that get the most blood flow: the liver and the brain.
酒精从血液进入身体器官，尤其是血液流动较多的器官：肝脏和大脑。
It hits the liver first, and enzymes in the liver break down the alcohol molecule in two steps.
酒精首先到达肝脏，肝脏中的酶类物质分两步分解酒精。
First, an enzyme called ADH turns alcohol into acetaldehyde, which is toxic.
首先，乙醇脱氢酶将酒精转化为有毒的乙醛。
Then, an enzyme called ALDH converts the toxic acetaldehyde to non-toxic acetate.
接着，乙醛脱氢酶将有毒的乙醛转化为无毒的醋酸盐。
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.
随着血液的循环，肝脏持续分解酒精，而分解乙醇的第一步决定了有多少酒精会到达大脑和其他器官。
Brain sensitivity is responsible for the emotional, cognitive, and behavioral effects of alcohol -- otherwise known as drunkenness.
酒精对情绪、认知和行为的影响--也就是我们常说的醉态--都是由大脑敏感程度决定。
Alcohol turns up the brain's primary brake, the neurotransmitter GABA, and turns down its primary gas, the neurotransmitter glutamate.
酒精会给大脑踩刹车，即提升氨基丁酸水平，使大脑更镇静；同时给大脑松油门，即降低谷氨酸水平，减弱兴奋度。
This makes neurons much less communicative, and users feel relaxed at moderate doses,
这会让神经细胞活跃度降低，适量摄入酒精使人感觉放松，
fall asleep at higher doses, and can impede the brain activity necessary for survival at toxic doses.
大量摄入则会陷入睡眠，而过量摄入可能抑制大脑生存所必须的活动。
Alcohol also stimulates a small group of neurons that extends from the midbrain to the nucleus accumbens, a region important for motivation.
酒精也会对一小部分神经细胞有激活效果，并从中脑持续到伏隔核区域，而伏隔核在奖赏和快乐等感官体验中具有重要作用。
Like all addictive drugs, it prompts a squirt of dopamine in the nucleus accumbens which gives users a surge of pleasure.
和所有成瘾性药物一样，酒精可以提升伏隔核中的多巴胺含量，使饮用者产生愉悦感。
Alcohol also causes some neurons to synthesize and release endorphins.
酒精还能使部分神经细胞合成并释放内啡肽。
Endorphins help us to calm down in response to stress or danger.
内啡肽可以帮助我们在面对压力和危险时保持镇定。
Elevated levels of endorphins contribute to the euphoria and relaxation associated with alcohol consumption.
摄入酒精后的愉悦与放松感正是由于内啡肽水平的上升。
Finally, as the liver's breakdown of alcohol outpaces the brain's absorption, drunkenness fades away.
最后，当肝脏分解酒精的速度超过了大脑吸收的速度，醉意就逐渐散去了。
Individual differences at any point in this journey can cause people to act more or less drunk.
整个过程中不同个体间的任何差异都会造成每个人醉酒程度的不同。
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.
比如，体重相同的一男一女在进食情况相同的情况下摄入等量酒精，最终血液中的酒精浓度仍然会有差异。
This is because women tend to have less blood -- women generally have a higher percentage of fat, which requires less blood than muscle.
这是因为女性体内血液含量较少--一般而言女性脂肪含量高于男性，而脂肪所需血液少于肌肉。
A smaller blood volume, carrying the same amount of alcohol, means the concentration will be higher for women.
等量的酒精和较少的血液，意味着女性血液中的酒精浓度会更高。
Genetic differences in the liver's alcohol processing enzymes also influence BAC.
肝脏中分解酒精的酶类与遗传有关，这也会影响血液酒精浓度。
And regular drinking can increase production of these enzymes, contributing to tolerance.
定期饮酒可以提高这类酶的产生水平，对分解能力有所帮助。
On the other hand, those who drink excessively for a long time may develop liver damage, which has the opposite effect.
另外，长期过度饮酒的人，肝脏可能会受损，从而产生反效果。
Meanwhile, genetic differences in dopamine, GABA, and endorphin transmission may contribute to risk for developing an alcohol use disorder.
同时，多巴胺、氨基丁酸、内啡肽传导的遗传性差异可能会增加酗酒的风险。
Those with naturally low endorphin or dopamine levels may self-medicate through drinking.
先天内啡肽或多巴胺水平较低的人，可以通过饮酒进行自我治疗。
Some people have a higher risk for excessive drinking due to a sensitive endorphin response that increases the pleasurable effects of alcohol.
也有人可能由于对内啡肽的敏感度较高，提升了酒精带来的愉悦感，从而导致过量饮酒的风险升高。
Others have a variation in GABA transmission that makes them especially sensitive to the sedative effects of alcohol,
还有人会因为氨基丁酸传导的变异，导致对酒精的镇静作用非常灵敏，
which decreases their risk of developing disordered drinking.
而这会降低他们酗酒的可能性。
Meanwhile, the brain adapts to chronic alcohol consumption by reducing GABA, dopamine, and endorphin transmission, and enhancing glutamate activity.
同时，大脑为了适应长期的酒精摄入，会降低氨基丁酸、多巴胺及内啡肽的传递水平，并提升谷氨酸盐的活动。
This means regular drinkers tend to be anxious, have trouble sleeping, and experience less pleasure.
这意味着经常喝酒会让人变得焦虑、产生睡眠障碍，且较难产生愉悦感。
These structural and functional changes can lead to disordered use when drinking feels normal, but not drinking is uncomfortable, establishing a vicious cycle.
当喝酒感觉很正常，不喝酒反而不舒服时，这种结构性和功能性的变化可能导致酒精滥用，因此陷入恶性循环。
So both genetics and previous experience impact how a person experiences alcohol
总而言之，遗传因素和过往经验都会影响个体对酒精的反应，
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.
也就是说有一些人在喝酒后会比其他人有更明显的反应，而长期酒精摄入会导致神经系统和行为发生变化。
