Absorption to Excretion: 

• Neurons: The two blue shapes labeled "Neuron A" and "Neuron B" represent nerve cells in the brain. Neurons communicate with each other through neurotransmitters and receptors.

• Adenosine Receptors: The green shape represents an adenosine receptor on the surface of a neuron. Adenosine receptors play a role in promoting sleep and relaxation.

• Adenosine Binding: Normally, adenosine (a neurotransmitter represented by the yellow shape) binds to its receptors, leading to feelings of sleepiness.

• Caffeine Blocking: Caffeine (represented by the red shape) has a similar structure to adenosine, allowing it to bind to adenosine receptors and block them. When you click the "Show Interaction" button, the illustration shows caffeine replacing adenosine and blocking the receptor (which turns gray).

• Resulting Effects: By blocking adenosine receptors, caffeine reduces the calming effects of adenosine, leading to increased alertness and wakefulness.

This illustration provides a simplified and visual representation of a complex biological process. It's designed to help users understand how caffeine works in the brain at a basic level.