I always enjoy your weblinks. Keep them coming. Interpreting them sometimes is confusing...for everyone. Some studies are very technical, and some use medical jargon.

The word epithelial is not limited to only certain places. Epithelial cells are everywhere in the GI tract. They are the first cells, that separate the body
from the environment. They are part your skin and all mucous membranes.

Your first quote is confusing too. Since zinc chloride and zinc proprionate are not commonly available as supplements. The article would have been more interesting and useful if it compared zinc sulfate, zinc oxide and zinc monomethionine. These latter 3 are typically used in humans. Also often the differences in mineral absorption many be very small. Here is an example:
Calcium Citrate is advertised as "more absorbable"..and it is. By a couple of percentage points only compared to calcium carbonate. This may be in reality of little consequence to the body, when calcium is needed. What calcium citrate IS important for, is for patients who are prone to calcium oxalate kidney stones. But you don't see THAT advertised at all!

We are sort of stuck with the studies that exist because in the supplement world there is not alot of funding for anything! Much of what I see in studies for example comes from Europe...because in USA the drug companies do not want us to know about other ways of improving health, and federal funding was cut several years ago. Some universities still do studies but they are less common that drug company funded studies. Also some studies on minerals, vitamins concern ANIMALS, vet uses, because the food industry gives things to them in feed, to improve meat quanitity and quality. For example I see alot of poultry studies.

Zinc is awful to take in the wrong form. So if zinc monomethionine shares good absorption with others, and does not cause nausea/vomiting, well, I think that is a plus. Zinc Picolinate also is easier. I personally like the OptiZinc since it also includes a small amount of copper, to offset any changes to the copper/zinc ratios.