I believe the answer to your question will be all of the above.
Answer:
Adenosine.
Explanation:
Adenosine is a neurotransmitter that is created in the brain and when it binds to the adenosine receptors, it slows down nerve activity and it creates a sensation of drowsiness.
<u>Caffeine</u> looks like adenosine to the receptors, therefore, when we have caffeine, <u>it binds to these receptors and there is no room left for the adenosine to bind</u>. However, the caffeine doesn't slow down nerve activity but, in the contrary, it speeds it up.
Therefore we can tell that caffeine blocks the receptors for the adenosine thus promoting wakefulness.
With doctors and nurses as well as patients (or parents of the patients) who understand the medical terminology you are using
The arteries carry oxygenated blood away from heart and then re-takes it back to your system
