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Originally Posted by geokker
I thought the gastrointestinal tract is really outside the body - we're tubes.
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Yeah, I've heard that too, but I personally don't buy it. Here's my reasoning.
Both our anterior and posterior openings are closed virtually all of the time. When they are, the GI tract is basically an elongated cavity running from one end to the other our body: it is totally inside of us, sealed off completely from the outside world. And anything within it, like food (a bolus or chyme) is also completely inside of it, and therefore, completely inside of us. In addition, we also a series of sphincters (such as the cardiac and pyloric sphincters) that close off subsections of the GI tract to form individual sealed-at-both-ends elongated subcavities.
If we walked around all day with our mouths, anuses, and sphincters all open, such that food could pass directly through our entire GI tract without running into any closed opening, then the idea that things inside our GI tract weren't actaully in our body might work for me. But under normal conditions, that isn't the case and I don't buy it.
