Eli5: How does the colon “know” what to absorb. Seeing as it can absorb dissolvable content inserted there. What prevents it from just reabsorbing all the fecal content?

Question

Eli5: How does the colon “know” what to absorb. Seeing as it can absorb dissolvable content inserted there. What prevents it from just reabsorbing all the fecal content?

In: Biology

Answer 1

Think of your digestive system as a really large puzzle. When food and nutrients come in that your body needs, they “fit” into the puzzle. All the food and fiber that is not needed to fill out the puzzle is the remaining fecal content. It’s not absorbed because there are no “puzzle pieces” to fit it to, I.e it’s not needed for a biological function.