As I understand it, most substances need help to pass through the walls of the intestines.
For example, in hepatic recirculation (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781307/) bile salts are grabbed and transported across the intestinal membranes by particular polypeptides.
Is there a summary of the sorts of things that can be transported across intestinal membranes? For example, hormones, stearates, lipids, etc. What general classes of molecules can pass the membrane and what cannot?
I am not looking for an exact answer, but a general characterization of major classes of organic molecules and their ability to pass through intestinal membranes into the body.