Just a Wonder

A row of bottles on my shelf
Caused me to analyze myself.
One yellow pill I have to pop
Goes to my heart so it won't stop.
A little white one that I take
Goes to my hands so they won't shake.
The blue ones that I use a lot
Tell me I'm happy when I'm not.
The purple pill goes to my brain
And tells me that I have no pain.
The capsules tell me not to wheeze
Or cough or choke or even sneeze.
The red ones, smallest of them all
Go to my blood so I won't fall.
The orange ones, very big and bright
Prevent my leg cramps in the night.
Such an array of brilliant pills
Helping to cure all kinds of ills.
But what I'd really like to know...
Is what tells each one where to go!