I have happened upon the sentence with the phrase of outside that I cannot understand in Crash Course Anatomy & Phisiology. It is at around 4 minut and 36 second. Here it goes:

Your digestive tract is really one unbroken, insulated tunnel of outside that just happens to run through your body.

It seem that the word outside was used there as an adverb,and not a noun because there is no article. Could you please rephrase the sentence for me?

  • I think the intended meaning is "insulated tunnel of outside stuff/things". The digestive tract is inside your body, but what is in it comes from the outside and goes back out again (in a general sense anyway). Like the outside air inside of a straw.
    – user3169
    Mar 25, 2018 at 19:04
  • 1
    Outside is being used as a noun. You might also say "The outside surface of your body includes the walls of the digestive tract." or "Even though your digestive tract appears to be inside you, it is actually outside you." In other words, you are topologically a torus or doughnut. Mar 25, 2018 at 20:44

1 Answer 1


It's probably not the best sentence in the world as there is no determiner or adjective. Perhaps it would have been better to replace "of outside" with "of your exterior". However, "outside" is definitely a noun here. Consider the M-W definition of "outside": "a place or region beyond an enclosure or boundary".

Now, consider your body as a cylinder that has been cored through the axis. The outside includes the volume "inside" the ring. This is the tunnel of "outside" that is inside of your body. Have a look at the graphic at: http://masculon.com/fitness/your-intestinal-tract-is-actually-outside-your-body/

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