Caffeine and Adenosine
咖啡因與腺苷
Why do so many people consume so much caffeine? Why does caffeine wake you up?
為什麼這麼多人攝取那麼多的咖啡因？為什麼咖啡因為讓你保持清醒？
By understanding the drug's actions inside the body you can see why people use it so much.
透過了解咖啡因在體內的反應你就能了解人們為什麼這麼大量的使用了。
In the HowStuffWorks article How Sleep Works, the action of adenosine is discussed in detail. While it sounds like advanced science, it's really pretty simple.
在 HowStuffWorks 所寫的 How Sleep Works文章裡頭，腺苷的作用有詳細的討論。
As adenosine is created in the brain, it binds to adenosine receptors. The binding
of adenosine causes drowsiness by slowing down nerve cell activity.
當腺苷在腦部產生時，會與其受體結合。腺苷的接合緩慢了神經細胞的活性造成睡意
In the brain, adenosine binding also causes blood vessels to dilate, most likely to let more oxygen in during sleep.
在大腦裡，腺苷接合也會造成血管的擴張 致使較多氧氣可以在睡眠時進入。
To a nerve cell, caffeine looks like adenosine. Caffeine therefore binds to the adenosine receptor. However, it doesn't slow down the cell's activity like adenosine would.
神經細胞會把咖啡因看成腺苷一般。造成腺苷的受體與咖啡因結合。然而這不會像腺苷一樣減緩神經細胞的活性。
As a result, the cell can no longer identify adenosine because caffeine is taking up all the receptors that adenosine would normally bind to.
因此，由於咖啡因佔去所有的受體，不能讓腺苷正常的接合，進而使細胞再也無法辨識腺苷了。
Instead of slowing down because of the adenosine's effect, the nerve cells speed up. Caffeine also causes the brain's blood vessels to constrict, because it blocks adenosine's ability to open them up.
反之，原本要因腺苷出現減緩，細胞卻加速了起來。咖啡因也造成大腦血管的收縮，因為他封鎖了腺苷放鬆血管的能力。
This effect is why some headache medicines like Anacin contain caffeine -- if you have a vascular headache, the caffeine will close down the blood vessels and relieve it.
這個反應就是為什麼一些頭痛的藥物如Anacin會摻入有咖啡因，如果你有血管性頭痛咖啡因會縮小血管而紓緩它。
So, now you have increased neuron firing in the brain. The pituitary gland sees all of this activity and thinks some sort of emergency must be occurring,
所以，現在你的大腦神經元發射頻率增加了，而腦下垂體發現了這些活動以為發生了什麼緊急事故
so it releases hormones that tell the adrenal glands to produce adrenaline (epinephrine). Adrenaline is the "fight or flight" hormone, and it has a number of effects on your body:
就此釋放的荷爾蒙來告訴腎上腺製造腎上腺素。腎上限速視"戰或逃"的荷爾蒙，它對身體有幾種反應
Your pupils dilate.Your breathing tubes open up (this is why people suffering from severe asthma attacks are sometimes injected with epinephrine).Your heart beats faster.
你的瞳孔會放大，你的呼吸道會打開（這就是為什麼氣喘病患發作有時要注射腎上腺素的原因）你的心跳加速。
Blood vessels on the surface constrict to slow blood flow from cuts and also to increase blood flow to muscles.Blood pressure rises.Blood flow to the stomach slows.
血管表面緊縮減緩血流以應付外傷並且增加肌肉的血流量。血壓上升。胃部血流減慢。
The liver releases sugar into the bloodstream for extra energy.Muscles tighten up, ready for action.
肝臟釋放肝糖到血液裡以供額外的能量。肌肉緊繃以準備行動。
This explains why, after consuming a big cup of coffee, your hands get cold, your muscles tense up, you feel excited and you can feel your heart beat increasing.
這解釋了喝完一大杯咖啡後你的手為什麼會感覺冰冷，心跳會增加
In the next section, we'll go into detail about caffeine's long term effects on the body.
再下一部分裡，我們將更深入咖啡因對人體會產生的永久效應。
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