There's the peritoneum which lines the abdominal cavity.

It's got a bunch of blood vessels to exchange chemicals so it's common to do kidney dialysis right into the abdominal cavity instead of the blood directly. Unlike hemodialysis, the machines can be taken home and operated by the patient.

And in vaginoplasties when they don't have enough tissue to do just a penile inversion, they can now pull through the peritoneum to help construct the vaginal canal instead of doing a colon graft.

Sometimes you can have hernias that you don't notice (and don't pose an immidiate health risk) until they get irritated or damaged. This can happen when a hernia is small(ish) and only contains fat from inside your abdomin.

These hernias can exist from when you were born as well. So you may never have had the tissue there to hold everything inside inside.

You can get these hernias fixed (and you should) but in a lot of cases (unless they get trapped intestine in them) they are considered "elective surgeries". What this means is that unless they are actively hindering your life then your health insurance is likely to be a bastard about paying for it.

I unfortunately learned all of this from finding a small hernia because it got really painful after I got pneumonia a few years ago. We found 4 hernias but only 1 was causing pain so my insurance only covered the surgery for 1. So I've got 3 more that are just ticking time bombs.

please report any undocumented features so that they may be deported out of your cavities