Hemoglobin Highway Phineas and Ferb

Just the two of us
In an esophagus
It's time to get this mission rolling
I don't wanna make a fuss
But that was pancreas
Look down before we reach the colon
On the Hemoglobin Highway
In a mini submarine (mini submarine)
If your going my way
You'll see what I mean
Take a left at the spleen!