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

Poop is what’s left *after* the colon absorbs what it can. It doesn’t “know” how to do anything, it just absorbs what’s absorbable until it reaches equilibrium with whatever that component is in the lining.