A great deal - a vast deal . . .
If you are a doctor, you, (hopefully) will have a very clear map of your own and other peoples' internal organs, lymph system, blood vessels, skeleton and so on - the rest of us . . . a vague notion of where one's heart, lungs and liver are, and probably not much than that.
It's weird to think of all these unknown miles of gut and vessels doing their thing, keeping you going, and not really knowing how any of it actually works or where it is placed in the body. I probably, even after not living there for some years, have a better idea of London's layout than where any of my lymph glands are, or what any of them look like.
Talking of glands . . . do you know where your adrenal glands are? those such vital things that control and deal with stress, flight or fight, etc. I didn't know until I stared reading about what happens when they become depleted - vaguely thought they must be somewhere in the neck. Nope . . . they sit snugly on top of the kidneys, and are complex/vital in operation and most often overlooked.
After a boring bout of Trigeminal neuralgia, which is still wobbling on slightly, I'm still trying to figure out what IT likes and doesn't, so started researching more into diet, stress, exercise, etc, and found out some fairly amazing stuff.
Sadly IT doesn't like me sitting too long at the computer, so I'll go and clean out the shed instead, but if you are as interested as I was, here's the rather wonderful Dr Berg explaining about how these Toblerone-shaped wonderments work.