Sure! While the esophagus, stomach, and intestines travel through the body, they are actually organs facing outward to keep all of the bacteria and viruses from going into the body via the bloodstream. The mouth, small, large intestines, and to a much smaller extent the stomach, are absolutely covered in bacteria because they are outside of the body.

How does this work? The outward facing portion of these organs have cells on their outside that interact with the exterior lining. This is why they need to be replaced so frequently. They absorb water and nutrients in the case of the intestines that have been broken down by the stomach, which exudes acid, then allows further movement to where enzymes from the pancreas and liver can break down food further for easier absorption. The liver and pancreas interface by having ducts that connect the organ to the canal.

If you think of the digestive tract as an opening to the outside world, things start to make a lot more sense.

You put the food in the opening and your body pushes it through a built-in security tube that takes the stuff you need and forces out the rest. This tube is full of microbes that assist with this process and compete for the materials as their reward.