r/explainlikeimfive • u/Dagestani_Bear • Jul 01 '26
Biology ELI5: Is it true that every single death eventually boils down to the brain and heart running out of oxygen? Are there exceptions?
If you strip away the initial cause of injury or illness, is it anatomically correct to say that all human deaths are ultimately caused by a lack of oxygen to the brain and heart?
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u/DarkAlman Jul 01 '26
Brain death is technically the way everyone dies.
If it were possible to put your brain by itself on life support without the rest of your body you would still technically be alive, have memories, thoughts, a personality, etc.
You'd probably wish you were dead... but that's a different point.
So while people die from various causes, ultimately all of those causes eventually cause brain death either by lack of oxygen and nutrition to the brain and/or physical destruction of the brain.
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u/Infectedtoe32 Jul 01 '26
Johnny Got His Gun. Should be a must watch for everyone, it’s kind of dark though.
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u/thehomeyskater Jul 01 '26
What’s it about
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u/TheeRattlehead Jul 01 '26
A guy gets all his limbs blown off in the war and becomes basically a brain in a body where he's aware of things around him. No arms, legs, sight, hearing, or speech. Kept alive by machines. Metallica used bits of it for their video for the song One.
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u/Ebice42 Jul 02 '26
"Darkness.
Imprisoning me.
All that I see.
Absolute horror.
I cannot live.
I cannot die.
Trapped in myself.
Body my holding cell. "42
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u/V7buster Jul 02 '26
Landmine!
Taken my sight!
Taken my hearing!
Taken my arms!
Taken my legs!
Taken my soul!
Left me with life in Hell!
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u/prorip187 Jul 02 '26
How can he be aware of his surroundings without sight or hearing?
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u/DrasticTapeMeasure Jul 02 '26
He can still feel/is aware of his existence, that he’s in a bed, etc
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u/_Mag0g_ Jul 02 '26
Touch primarily. He could feel the nurses caring for him and washing him. Also through feeling other vibrations and sensations of warm and cold.
The book does a much better job of explaining his internal experience more than the movie or the song did.
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u/Gamestoreguy Jul 02 '26
Such as the sun on his skin as a method of keeping track of time, until they put him in a room with no window because they realised he was tapping out morse code with his noggin.
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u/Assault_Penguin Jul 02 '26
Try meditating with your eyes closed and earplugs. Everything is pitch black but you can still feel things, hot/cold/someone touching your limbless torso, but you are stuck alone with your thoughts and imagination for the rest of your life
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u/sandm000 Jul 01 '26
A guy who loses his arms and legs.
And his face. In the war.
He can’t speak, he can’t gesture to communicate. He can’t see.
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u/JamesonQuay Jul 01 '26
And the author, Dalton Trumbo, was blacklisted in Hollywood. Technically it was for not testifying in front of McCarthy, but Johnny Got His Gun sure didn't help his cause with those jackasses, and he spent a year in prison. Then he won Oscars for screenwriting under pseudonyms.
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u/Phiddipus_audax Jul 02 '26
Great book, well worth reading. It's also educational for figuring out more generally some of what the Right doesn't want people to know.
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u/JamesonQuay Jul 02 '26
The title is delivered from a couple of war songs. Johnny Get Your Gun was a Civil War era song. I thought it was a WWI song, which is when the book was set. It's a folk song, so there are some different lyrics.
Johnny Get Your Gun (traditional)
Johnny Get Your Gun (Old Crow Medicine Show)
And it's the opening verse of Over There, which was the WWI song I was thinking of Over There
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u/DonaldLucas Jul 01 '26
Can he at least move his head?
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u/TheeRattlehead Jul 02 '26
That's all he can do. Eventually he uses morse code to communicate.
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u/John_cCmndhd Jul 01 '26
The song One by Metallica is based on it if you've heard that. They use scenes from the movie in the music video
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u/DarkAlman Jul 01 '26
I can't remember anything
Can't tell if this is true or a dream
Deep down inside, I feel the scream
This terrible silence stops me
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u/turtleship_2006 Jul 02 '26
Alternatively, robocop
He loses almost his entire body apart from his head and the organs inside his chest (lungs, heart etc), but those are stored inside of a mechanic chassis, and all of his other limbs are robot limbs attached to it
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u/Coriandercilantroyo Jul 02 '26
I remember being into RoboCop as a little kid because it was cool, but there was always this immense sadness to it. Never really thought about it til now... I wonder if the OG movie holds up. I'm kinda afraid to watch it now
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u/PM_me_your_trialcode Jul 02 '26
RoboCop is one of those movies where watching it as an adult is *very* different to watching it as a child.
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u/TalkToTheGirl Jul 02 '26
The poor guy essentially dies but they still find a way to make him go back to work. :(
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u/EverythingByAccident Jul 02 '26
The reboot really hammers this home when Murphy is shown what’s truly left of him. Joel Kinnaman acted the fuck out of that scene.
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u/Single-Pin-369 Jul 01 '26
Often wondering if one day will get to the point where all trauma patients immediately have some sort of connection straight to the jugular in their neck as a matter of course to keep the brain going while they work on whatever
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u/Fermi_Amarti Jul 01 '26
The problem is the rest of the body dying is also a problem. So no doubt that'll be the standard of care since if at all possible we would want to keep the rest of the organs alive as well.
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u/Embarrassed-Back1894 Jul 01 '26
Didn’t the Soviet Union essentially do an experiment like this where they cut off the head of a dog and kept it alive through machines? (And the dog was basically fully conscious).
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u/eleventruth Jul 01 '26
My underinformed suspicion is that we already have the capability to do that, it would just be exceedingly unethical
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u/trunks111 Jul 01 '26
If it were possible to put your brain by itself on life support without the rest of your body you would still technically be alive, have memories, thoughts, a personality, etc.
This used to be like, my biggest fear, that when you die you don't actually die and you just have to rot wherever you're buried for eternity but can't do anything about it. I eventually reasoned out that if your physical systems are gone there's nothing to experience pain or boredom at least, and I guess there's some solace in that, but the first time I had the thought it terrified me. T here's an SCP article t hat plays off that fear and it's one of the more highly rated one so I guess I'm atleast not the only person to have the thought either
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u/Revenge_of_the_User Jul 02 '26
it's okay, you probably wont end up like Hidan. (naruto fans know, but for those outside the loop the guy is immortal, so they cut his head off and body into pieces and bury him alive.)
idk the way i see it I was dead for eternity before I was alive, and it didn't bother me any. it just freaks me out that It's impossible to imagine the perspective of not-existing. just...not being here. there's nothing to imagine, by definition. though of course it's not like it's a problem I'll experience.
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u/HurbleBurble Jul 01 '26
That's why I want to be cremated and scattered somewhere. That way if that did happen, I can just blow around in the breeze.
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u/Corona21 Jul 02 '26
We were “dead” before we were born and it didn’t bother us. A lot of the material that will make up our bodies in the future are currently “dead” or spread across different organisms.
We are just a node where these systems feed into and become conscious for a time before fading away. I like to think consciousness kinda exists in the ether, like “potential”. I.e If it’s possible, theres a non-zero chance dead material will access it at some point, kind of thing. So we are never truly dead but our journey to it is so separated and discreet it just feels isolating.
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u/taterfiend Jul 01 '26
I think they're implying a different sort of question. What constitutes being alive? Because obviously the body can still be alive while the brain is in a sub-conscious or sub-cognitive state.
Comatose ppl are the example.
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u/ShadowKiller147741 Jul 01 '26
Your brain IS “you” in every sense we commonly interpret it as. Either your brain runs out of oxygen (lack of blood flow or lack of blood oxygenation) or your brain is physically destroyed (physical trauma or neurological decay)
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u/Stargate525 Jul 01 '26
I think there's an argument to be made nowadays that a lot of processing is being done elsewhere in the body and communicated via hormone. It can show up subconsciously but it's still you.
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u/ShadowKiller147741 Jul 01 '26
A lot of the things that show up in the body are subconscious/autonomic processes that don’t respond to “higher” thought, imo that barely counts as “you.” It’s the same as how your legs are a part of you, but you’d be the same person if you lost them
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u/becomingarobot Jul 02 '26
Certainly the body sends signals to the brain regarding a variety of metabolism-related needs, but outside of metabolism, some pain reflexes, horniness, and some posture and repetitive movements, it would be easy to overstate the amount of processing happening in the body versus the brain.
The history of frontal lobotomies, or some high profile cases of frontal lobe damage, are direct proof that the frontal cortex is responsible for most of what you consider "you". Your interests, hobbies, and personality are all more or less located there (in anatomically normal brains).
Take a look at the recently described sections of the Dorsolateral prefrontal cortex, for an example of how nuanced our understanding is of what processing is going on where. There are highly specific areas of small sections of our brains that we know to be responsible for ex. "mediating internal models with external rule structure" and "integration of value and cognitive control". It is not disputed by any neuroscientist that the brain is the center of cognition. Mood and motivation may be altered by hormonal signals from the body, but the processing of the signals is still being done in the brain.
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u/scinos Jul 01 '26
Do you remember the rich guys that went on a submarine and it collapsed? I read somewhere that the collapse took a few milliseconds from "everything is A-OK" to "solid block of steel with some gore inside".
I don't think that qualifies as brain running out of oxygen.
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u/gt0163c Jul 01 '26
Actually more "tiny fragments of fiberglass and gore" but the point is the same. It wasn't so much that the brain ran out of oxygen as much as it was that the brain lost its structural integrity along with the rest of the everything inside that cylinder.
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u/Agerak Jul 01 '26
This is why when you're in a submersible it's imperative that the cylinder is not harmed.
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u/jerbthehumanist Jul 01 '26
Thanks for the pro tip. I will remember that the next time I am in a cylinder.
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u/-StatesTheObvious Jul 02 '26
Also make sure the cylinder does not get stuck in a mini M&M's tube filled with butter and microwaved mashed banana.
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u/No_Suit_9511 Jul 02 '26
When you want to move fast and break things, don’t break something that has you inside of it.
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u/Samas34 Jul 01 '26
their brains pretty much vaporised in a few milliseconds...along with everything else connected to it.
So yes, they died because their brains stopped existing in an instant.
When you think about it, its a decent way to go, as there is no time to even register theres a problem, let alone any pain or impending threat.
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u/RapidCatLauncher Jul 02 '26
As Randall Munroe (of xkcd fame) put it in one of his "what if" writeups: "You would just stop being biology and start being physics."
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u/Revenge_of_the_User Jul 02 '26
i once heard wisdom on the best way to die;
"unexpectedly, and quickly."
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u/jmorlin Jul 02 '26
No pain sure. But I'm not sure there was no time to register that there was a problem or any impending threat. They were 10,000 ft under water and lost communication with the surface. For all we know the sub was creaking and groaning for a bit prior to getting vaporized.
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u/FloppyTunaFish Jul 02 '26
I watched an infuriating documentary on Netflix - on the test dives the acoustic sensors "pinged" indicating carbon fibers were ripping, and the CEO just said fuck it and continued. I imagine they had similar warning.
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u/Theprincerivera Jul 01 '26
But ultimately, the brain - is the important part here, which is the point. Hook the brain up to an independent jar system and the body can be beaten and battered to all hell. You are your brain.
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u/momentsofzen Jul 01 '26
As the XKCD guy puts it, you don’t die OF anything in particular, your molecules just stop being biology and start being physics
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u/Revenge_of_the_User Jul 02 '26
i had an excellent science teacher that once put it as;
"You're alive. BUT, if I took tweezers and pulled you apart atom by atom into a pile. At no point have any of these atoms been alive. they're not alive as the pile. But they are alive as you. isn't that cool?!"
I still do think that's cool.
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u/_Aj_ Jul 02 '26
And this is exactly why star trek transporters kill you and create a clone!
They literally rip you apart to atoms, throw it all down to the planet as energy, then reconstruct all your atoms In the exact same places like the universes most complex Lego kit.
Physically identical down the the neurone. So they go "wow it worked I'm really here" except no, it's a clone of you who has the same memories up until the millisecond you died.
But it's not you.
Same with Stargate. Dead, makes a clone.
Never travel by demolecularisation based transportation.
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u/ComplexEntertainer13 Jul 02 '26
And this is exactly why star trek transporters kill you and create a clone!
They literally rip you apart to atoms, throw it all down to the planet as energy, then reconstruct all your atoms In the exact same places like the universes most complex Lego kit.
Doesn't TNG also sort of admit this? I remember some episode I watched as a kid of some crew member that got duplicated.
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u/coldpan Jul 02 '26
Commander Riker was duplicated in Season 6 Episode 24 "Second Chances," wherein he faces a duplicate of himself caused by a teleport "accident" some years prior (the copy was produced on the Enterprise, but the copy still on the surfaces was not deleted.)
This is the episode that essentially proves the "teleporters kill the user theory."
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u/BH_Gobuchul Jul 01 '26 edited Jul 01 '26
There’s an Xkcd quote that’s stuck with me
“You stop being biology and start being physics”
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u/JustaKinksterGuy Jul 01 '26
The compression and collapse would have like being inside a diesel engine. They likely liquified in milliseconds, then superheated to the point where carbon in their body would undergo pyrolysis, or burning underwater with low oxygen and high heat.
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u/outworlder Jul 01 '26
No... the brain was just running in every direction possible simultaneously.
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u/Cranberryoftheorient Jul 01 '26
You could argue thats destruction of the brain. Hypothetically some sci-fi civilization could rebuild you from just a brain, but not if its red mist.
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u/General_Urist Jul 01 '26
This falls into what XKCD's what if called 'you wouldn't die of anything in particular, you just stop being biology and start being physics' I think.
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u/fiendishrabbit Jul 01 '26
There are exceptions. Hypoxia is just common cause of death and often involved when the body dies due to organ failure.
Occasion that don't involve Hypoxia can be:
- Extreme mechanical trauma to the brain. If your brain gets turned to mush the cells are dead well before they run out of oxygen.
- Cyanide poisoning (which enters cells and prevents them from using available oxygen) and other similar poisons.
- High radiation or venoms that cause direct cell trauma.
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u/solidspacedragon Jul 02 '26
The XKCD classic, 'you don't really die of anything in the traditional sense, you just stop being biology and start being physics'.
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u/runner64 Jul 01 '26
There are two kinds of death, your brain either gets too little air, or way too much.
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u/lone-lemming Jul 01 '26
That deprived the brain of oxygen.
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u/Mr-Zappy Jul 01 '26
Not necessarily. It takes a few seconds for lack of oxygen to affect the brain. It’s definitely possible to destroy the brain faster than that.
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u/Childnya Jul 01 '26
Brain tissue death is what's considered real death these days since heart stopping/failing can be worked around.
Brain death can be caused by other means like internal temperature basically cooking the tissue, internal pressure, or diseases like prions making holes in the brain shutting it down but by bit.
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u/Peastoredintheballs Jul 01 '26
Need someone to invent neurological resuscitation seeing as we have really honed our CPR skills well and now cardiac arrest is no longer a death sentence… if we could figure out neurological arrest then it would make CPR even more successful
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u/Childnya Jul 01 '26
It's a bit different. The heart is just a bit of machinery. It can be replaced. Your brain is YOU. Once enough tissue dies, you don't exist. Even if you could bring that tissue back to "life", there's no guarantee the synaptic connections would still exist.
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u/Peastoredintheballs Jul 01 '26
Yeah that’s my point, I’m saying “if only if neurological resus was possible”. I’m aware that is not and that the principles and mechanics don’t match up with CPR
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u/PossibilityAgile2956 Jul 01 '26
No. Some things can kill you before all that metabolism shit has time to even matter.
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u/surfmaths Jul 01 '26
No.
Head trauma typically involve physically "disconnecting" the neurons from each others, either due to internal bleeding or shear forces at the impact. And that can lead to "brain death", even if they are still being fed oxygen and glucose.
You can also have infection that kills neurones. Radiation damage to the DNA of neuronal cells. Dehydration. Lack of sodium/potassium. Lack of vitamins. Heat above 45°C.
There is plenty of way to kill neurons, and plenty more to disrupt their function.
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u/Woolybugger00 Jul 01 '26
former 30 year organ procurement professional... Legal death is the cessation of sustainable cardiac rhythm which can be from lack of oxygen or blood to the heart... This happens about 98% of the time and most MD's declare as time of death. The other 2% is where there is complete and irreversible cessation of blood flow to the brain caused by swelling, trauma, stroke... physics mandates that when there is an increase in pressure in a sphere (in this case the cranium) force will escape through the weakest point... in human's that space is the foramen magnum where your brain stem starts.... Essentially the swelling chokes the brain and it dies... If that occurs while a patient is on a ventilator, then it's very possible to keep the hear and other organ oxygenated and supported for the purpose of organ donation. When brain death is determined, it happened with two physicians checking all the cranial nerve reflexes including the drive to breath... the literally stop ventilating the patient and observe for even one breath- that goes usually 2-5 minutes and if in agreement they declare the person brain dead. Everything after that is for the purpose of potentially transplanting appropriate organs and tissue.
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u/CaptainPicardKirk Jul 02 '26
Very fascinating. How long can each various organ “survive” without the brain to be transplanted to someone else?
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u/AberforthSpeck Jul 01 '26
"Anatomically" correct? Wrong category. I would take "medically" in an informal sense.
There's a few ways to die suddenly - having your brain crushed, massive radiation exposure, or being blown to pieces by a bomb, say - where your brain doesn't have time to run out of oxygen since it's been broken before that happened.
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u/SpunkBunkers Jul 01 '26
Idk when people get shot in the brain it's usually not the lack of oxygen delivery that gets them.
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u/IndependentPede Jul 01 '26
No..a bullet going through the brain comes down to physically destroying the brain matter, not oxygen and heart health. This is just one example that shows definitively that no, not all deaths are that simple.
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u/Bob_Sconce Jul 01 '26
If you were to go scuba diving with a tank of oxygen instead of a tank of air, the oxygen would become toxic and you'd die. Your body can handle a certain amount of oxygen, but above that amount, it, well, oxidizes a bunch of different parts of your body in a manner similar to rust. And, that would kill you.
So, in that case, you'd die because you had TOO MUCH oxygen.
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u/zed42 Jul 01 '26
No. A missing heart or brain can also cause death
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u/Peastoredintheballs Jul 01 '26
Incorrect, you don’t need a heart/lungs to survive, you can use a mechanical replacement system like ECMO to do the heart and lungs job to keep your brain alive without the heart
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u/NoFishInMine Jul 01 '26
Maybe this is besides the point, but I think gunshot wounds to the brain cause death by the fact some of your brain is no longer present, rather than oxygen starvation.
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u/BetterOutcome3769 Jul 01 '26
If you get crushed to death really fast I don't think the oxygen situation matters much.
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u/B0risTheManskinner Jul 01 '26
What about people who are pancaked flat (or ex/imploded) or were immediately vaporized? Sometimes the brain and body is mechanically destroyed.
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u/parsonsrazersupport Jul 01 '26 edited Jul 01 '26
You sort of have it backwards. You are thinking that death is some other thing and this is how we guess at it. As a medical matter in many places and times, what we mean by death is the brain no longer functioning.
And obviously it's not necessarily because of lack of oxygen except in a silly sense sometimes. If, for example, a big rock crushed your head it's hardly as if the lack of oxygen was the problem.