【英语时差8,16】咖啡因的作用

 Coffee And Caffeine: How Caffeine Makes You Feel More Awake Some people aren't able to function without that first cup of coffee in the morning. We'll look at how caffeine in coffee makes you feel more awake and alert. Soon after you drink a cup of coffee, caffeine, a strong stimulant¹ is absorbed into your intestinal² tract³ and into your blood. Peak absorption occurs in less than an hour, usually within thirty minutes. Once absorbed, it is rapidly distributed into all of your body’s fluids, then processed by your liver and eventually excreted in urine. Three hours after you drink a cup of coffee, the level of caffeine in your blood will be half of what it was at its peak. Six hours after drinking coffee, you will have eliminated most of the caffeine from your system. Once caffeine is distributed throughout the body, it stimulates⁴ your nerves and causes adrenalin to be released. Adrenalin is the main neuro-transmitter that changes your levels of energy and alertness. Adrenalin increases your heart rate, which results in more blood pumped per minute. This blood carries extra oxygen to your brain, making you feel more alert. Caffeine also directly stimulates the spinal⁵ cord and the cortex of the brain, which enhances these alert feelings. Many people experience a dip in energy several hours after drinking coffee. Though scientists aren’t exactly certain why this happens, a possible explanation may be that, after the effects of caffeine wear off, your brain needs to adjust to working without the stimulus⁶ the caffeine provided. So, though that first cup of coffee might get you going in the morning, it might also leave you feeling fatigued⁷ half way through the day.

1 stimulant   

n.刺激物，兴奋剂

参考例句：

• It is used in medicine for its stimulant quality.由于它有兴奋剂的特性而被应用于医学。
• Musk is used for perfume and stimulant.麝香可以用作香料和兴奋剂。

2 intestinal   

adj.肠的；肠壁；肠道细菌

参考例句：

• A few other conditions are in high intestinal obstruction. 其它少数情况是高位肠梗阻。 来自辞典例句
• This complication has occasionally occurred following the use of intestinal antiseptics. 这种并发症偶而发生在使用肠道抗菌剂上。 来自辞典例句

3 tract   

n.传单，小册子，大片(土地或森林)

参考例句：

• He owns a large tract of forest.他拥有一大片森林。
• He wrote a tract on this subject.他曾对此写了一篇短文。

4 stimulates   

v.刺激( stimulate的第三人称单数 )；激励；使兴奋；起兴奋作用，起刺激作用，起促进作用

参考例句：

• Exercise stimulates the body. 运动促进身体健康。 来自《简明英汉词典》
• Alcohol stimulates the action of the heart. 酒刺激心脏的活动。 来自《现代英汉综合大词典》

5 spinal   

adj.针的，尖刺的，尖刺状突起的；adj.脊骨的，脊髓的

参考例句：

• After three days in Japan,the spinal column becomes extraordinarily flexible.在日本三天，就已经使脊椎骨变得富有弹性了。
• Your spinal column is made up of 24 movable vertebrae.你的脊柱由24个活动的脊椎骨构成。

6 stimulus   

n.刺激，刺激物，促进因素，引起兴奋的事物

参考例句：

• Regard each failure as a stimulus to further efforts.把每次失利看成对进一步努力的激励。
• Light is a stimulus to growth in plants.光是促进植物生长的一个因素。

7 fatigued   

adj. 疲乏的

参考例句：

• The exercises fatigued her. 操练使她感到很疲乏。
• The President smiled, with fatigued tolerance for a minor person's naivety. 总统笑了笑，疲惫地表现出对一个下级人员的天真想法的宽容。