Microvilli - Distinction of Nutrients

[Satonam]

I've been reading about the human digestive system and diving deeper into the details, however I can't seem to find a webpage that answers my questions. All my current knowledge can be summed by these two links:

https://jonbarron.org/article/physiology-small-intestine-part-1
https://jonbarron.org/article/physiology-small-intestine-part-2

The epithelium in the small intestine is lined by villi and microvilli which are responsible for transporting nutrients, fats, lipids, sugars, amino acids, etc. However, each microvilli is specific to the nutrient it absorbs. What I'd like to know is, how do enterocytes differentiate between various nutrients and target them? I know, as per the article, that vitamins and minerals are absorbed indirectly; they latch onto fats and amino acids, which in turn latch onto sodium ions, and ride through the enterocytes and into the bloodstream like a trojan horse.

Reading this, it seems to me that the body doesn't "see" the fats or the amino acids, it only detects sodium -which happens to bind to these nutrients and conveniently reel them in. Furthermore, isolated minerals are actually treated as toxins by the body, they are also "unseen" by our metabolism; the only reason we absorb these minerals is because they hide in other nutrients. They're like refugees hiding in the trunk of your car to cross the border.

My question:

How do fat-enterocytes identify fats while amino acid enterocytes identify and target each individual amino acid? Are minerals somehow filtered too? Or can an Fe particle latch onto any fat or amino acid and ride them into the bloodstream indiscriminately through it's vehicle's specific gate?

 

[jim mcnamara]

Receptor sites in cell membranes on the villi:
They work on molecules, not particles. There is a sort of lock-and-key mechanism - as an analogy.
Here is a technical explanation for glucose absorption by villi in the small intestine:
https://www.ncbi.nlm.nih.gov/pubmed/14641013

Note: - the exact same lock-and-key system may work well for several different nutrients. Example: Cu, Zn, and ascorbates (vitamin C ester) all are picked up by the same transporter. So there can be "competition" for given receptor site. Taking a vitamin C pill floods the intestine with lots of ascorbate, which means the relatively very few Cu bearing molecules present may never get a ride out even though it is on the correct binder molecule. This explains why taking lots of vitamin C long term can cause a copper deficiency.