Caffeine is absorbed into the blood and body tissues with absorption virtually complete in around 45 minutes after ingestion. The peak plasma caffeine concentration is reached 15-20 minutes after ingestion.
In the brain, there is adenosine. It is an inhibitory neurotransmitter; it binds to adenosine receptors in the brain. This means adenosine can act as a central nervous system depressant. In normal conditions, adenosine promotes sleep and suppresses arousal by slowing down nerve activity. Adenosine binding also causes blood vessels in the brain to dilate, to increase oxygen intake during sleep. When awake, the levels of adenosine in the brain rise each hour.
To a nerve cell, caffeine looks like adenosine. Caffeine binds to the adenosine receptors. However, in contrast to adenosine, it does not decrease the cell's activity. As caffeine utilizes all the receptors
Caffeine blocks adenosine's ability to open up the brain's blood vessels, causing them to constrict-this is the reason caffeine is used in pain reliever medicine for headaches. If the headache is vascular, the caffeine closes down the blood vessels and gives relief.
With caffeine blocking adenosine, there is an increase in the firing of neurons in the brain. The pituitary gland observes the increased activity and perceives it as an emergency, 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 our body, such as dilates pupils, opens breathing tubes, increases heartbeat, constricts surface blood vessel, increasing blood pressure, slows blood flow to stomach, releases sugar from the liver into the bloodstream for extra energy and tightens muscles.
Caffeine is quickly and completely removed from the brain. Its effects are short lived, and it tends not to affect concentration or higher brain functions negatively. However, continued exposure to caffeine leads to the development of a tolerance to it.
33. What time does caffeine need to be absorbed perfectly?
A. 15 minutes.
B. 45 minutes.
C. 60 minutes.
D. 120 minutes.
E. 150 minutes.
34. Caffeine can be used in pain reliever medicine for headaches because
A. it decreases cell's activity
B. it releases sugar from the liver into the bloodstream
C. it increases oxygen intake during asleep
D. it opens breathing tubes
E. it blocks adenosine opening up the brain's blood vessels
35. "… with absorption virtually complete …" (Paragraph 2) What is the synonym of the underlined word?
A. Nearly
B. Slightly
C. Hardly
D. Rarely
E. Already
36. "… it does not decrease the cell's activity." (Paragraph 3)
what does 'it' refer to?
A. The brain
B. Blood vessel
C. Caffeine
D. Adenosine
E. Heartbeat
Caffeine is used in masses on a daily basis to increase wakefulness, alleviate fatigue and improve concentration and focus. When caffeine is consumed, it changes our brain and body work.
33. b
34. e
35. a
36. c
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