How does caffeine reach the brain after someone drinks a cup of coffee or tea? In your answer, be sure to identify the systems involved.

When we drink coffee, caffeine binds to our brain's adenosine receptors, preventing the chemical from binding with the receptors and making us tired. For those of us who regularly drink coffee in copious amounts, our brains develop more adenosine receptors, so it takes more coffee to keep us awake.

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