Home > Biology, chemistry, Science > Running for the shelter of everyone’s little helper.

Running for the shelter of everyone’s little helper.

November 23, 2009 Leave a comment Go to comments

This weekend while laid up with a cough, I experienced two of the different effects of caffeine. One of the effects was very welcome, as the caffeine in an excedrin helped to relieve my headache. The other effect wasn’t as welcome, when the same caffeine kept me awake for the next four hours. While I lay there, trying to fall asleep, I started to wonder how caffeine did what it did, and whether the reaction that reduced my headache was the same thing that kept me awake. Part, but not all, of what kept me awake also relieved my headache.

As we digest caffeine, it enters the bloodstream, because of it’s relatively small size caffeine is also able to pass through the blood-brain barrier. While in the brain, caffeine binds itself to adenosine receptors. Adenosine is found everywhere in the body and is important in ATP metabolism. In the simplest terms it is the last stage of turning the food that we eat into the energy that we use to function. In the brain, adenosine has a slightly different role by protecting the brain by suppressing neural activity, by doing this adenosine makes us drowsy. When caffeine binds to the adenosine receptors, which it’s able to do because of caffeine’s similar chemical structure to adenosine, it blocks adenosine from doing the same and prevents us from becoming drowsy. This is one of the ways in which caffeine works.

Since adenosine is naturally created by the body, when it’s not able to function as it normally does the body reacts. When caffeine takes the place of adenosine and block adenosine receptors, it doesn’t suppress neural activity like adenosine does. The body is used to this suppression, and when it doesn’t occur, the body reacts. The relative increase in neural activity, makes the pituitary gland believe that the body is in some sort of danger and activates the adrenal glands to release adrenaline. So caffeine delivers a one-two punch by first inhibiting drowsiness and then by releasing adrenaline which makes us more alert, along with several other side effects. One of the more important side effects is that the liver releases sugar to give the body extra energy.

This explains why caffeine makes us more alert, but doesn’t explains why it relieves headaches. One of the functions of adnenosine in the brain is to dilate blood vessels.  This is so that when we’re sleeping, and our breathing slows, the body is still able to get all the oxygen that it needs. Unfortunately, dilated blood vessels in the brain can become inflamed and create headaches. When caffeine binds to the adenosine receptors, they inhibit blood vessels from dilating. One of the other effects of adrenaline is that it constricts blood vessels, which further reduces headaches.

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