system
Given the following post, respond as if you're commenting on Reddit:
human
What fills the empty spaces in our bodies?

My question is one I've wondered about for quite a while.  Veins are, excuse the line, a series of tubes, so it's not like blood is just randomly filling in all of our cavaties.  I also imagine our organs don't just fit together like puzzle pieces, so there must be empty space in there somewhere.  What's it filled with?  I doubt some type of air, but am unsure what else it could be.  I know of nothing that  produces secretions just to "fill the gaps", but I'm not a biologist ;)  What's in there?

Thanks!
gpt
In the abdomen - fat, mostly. There's a small amount of fluid that helps lubricate things as they move around.

Some organs change shape and size (e.g. bladder, stomach, intestines), whilst others stay constant (e.g. liver). They do pretty much fit together like a jigsaw puzzle, with fat filling in the gaps.