system
Given the following post, respond as if you're commenting on Reddit:
human
How much of our bodies do we (humans) need to live?

I searched this question up and couldn't really find a definitive answer.

For example, if we lose a leg or arm, we can still very well live. How far does that go? Is it possible, like in some sci-fi movies, that we can "live" with just a brain and machine-fed nutrients? I know "live" is somewhat subjective, but let's say enough to think and perhaps communicate?
gpt
You can lose:

* 
Your limbs
* Your spleen
* Your gall bladder
* About 1/2 of your intestines
* Your reproductive organs, internal and external
* Your bladder 
* Your left lung (the right lung is bigger)
* One kidney
* One adrenal gland
* Lobes of your brain.  The frontal lobe is considered a 'non-eloquent' region, meaning that limited damage is not associated with massive neurological deficits.

and be more or less OK.  Now, there are other things that can be compensated for.  They are:

* Second kidney (dialysis)
* Pancreas (enzyme and insulin replacement)
* Stomach (special diets, B12 replacement)
* *Second adrenal gland (with hormone replacement, thanks DocPsychosis)*


And there are some things which really can't be replaced in an effective way:

* Second lung
* Heart
* Liver
* Brainstem
* Rest of GI tract

There are ways to compensate for some of these (ECMO for heart/lung, total parenteral nutrition for GI tract), but they are not long-term solutions.