In a 2017 paper in Icarus, Schuerger and colleagues tested the survival of Bacillus subtilis, a well - studied bacterium found in human gastrointestinal tracts, in simulated Martian soils with various levels of saltiness. (sciencenews.org)
Overview of zinc absorption and excretion in the human gastrointestinal tract [review]. (kellymom.com)
The mucus layers secreted by the body to line the gut show a gradient of sialic - acid - capped mucins, with the concentration rising further along the human gastrointestinal tract. (sciencedaily.com)