What actually would happen to an unprotected human miles below sea level? How do certain fish survive w/o any reaction to the tremendous pressures?
Thanks dopes!!!
It’s not so much about what would happen when you’re down there, it’s the problems you have coming up.
Deeper you go, the more your lungs compress. Deep enough, your lungs collapse. Ultra-deep ‘free divers’ experience this, and survive, though they’re freakishly fit - far beyond your normal human. Deep enough, and you’re going to get very cold very quickly. Too deep, you’re never going to be able to recover in time - Probably suffer nitrogen narcosis, with hypothermia and hypoxia racing to kill you.
Fish don’t have any gas-filled organs except for swim bladder, so they don’t collapse. The swim bladder adjusts for bouyancy. Most fish are cold blooded, and hypothermia isn’t usually an issue for them.
Beyond that, dunno.
When humans go deep-sea diving and are exposed to the ambient sea pressure, they breathe compressed air to keep their lungs inflated against the surrounding pressure. However, because the air is compressed, you start to run into problems as the pressure increases. One problem is that the compressed air starts to dissolve in your bloodstream, so that if you ascend too quickly, the dissolved air can come out of solution, resulting in air bubbles in your bloodstream. 
This is bad, and is called the “bends.” (The blockages can duplicate symptoms of stroke, for example.)
Another problem is that if the compressed air contains the same proportions of oxygen and nitrogen as air at the surface, you start to get symptoms of nitrogen narcosis as you go deeper and the air pressure necessarily increases, the symptoms of which are similar to those of alcohol intoxication. You also start to get oxygen toxicity, because each breath contains several times the amount of oxygen at the surface–again, because the air is compressed.
These problems can be compensated by using exotic mixtures such as substituting inert helium or even hydrogen for some of the oxygen and nitrogen. The record for the maximum depth for a SCUBA diver using such a gas mixture is 330 meters (1,083 feet). The record for a diver being supplied from the surface with an exotic compressed gas mixture is 534 meters (1,752 ft).
Other medical problems have been noted at such depths, such as aseptic bone necrosis, joint osteonecrosis, and high pressure nervous syndrome.
Without some type of compressed air to keep the lungs inflated against the surrounding pressure, the lungs would simply collapse at great depths. Fish survive at such depths because they don’t have any significant air pockets inside of them. (I’m not sure if deep-sea fishes generally have swim bladders or not, but a bit of googling indicates the answer is “not.”)
There has been some thought that the compressed gas mixtures might be replaced with an even more exotic liquid (as seen in the movie The Abyss) but so far, this is just Hollywood fantasy.
A human exposed to sea pressure miles deep would have their lungs collapse and every other air-filled cavity in the body would be squashed. They’d also be dead, of course.
Not air, but specifically nitrogen. This happens even on shallower recreational dives (<100 feet depth).
Humans are not the only vulnerable ones: deep-diving sperm whales (which descend as far as 6000 feet) get the bends, too.
:smack: Thanks a lot guys. I guess the piece of the puzzle I was looking for was just as you stated…fish don’t have any gas filled organs whereas humans do, therefore would not be subjected to extreme pressures. That pretty much answers it. Great information!!
Some fish do not have any gas-filled organs. Others have a swim bladder, but they “use” it for buoyancy, not breathing. All fish are subjected to the extreme pressures, but since this doesn’t affect their breathing, they’re OK.
Humans have several gas-filled spaces in their bodies, such as our sinuses and Eustachian tubes. Those would be collapsed by extreme pressures. For everything except lungs that would be painful if not deadly. For lungs it’s deadly even at relatively shallow depths.
OP has been answered, but I need to straighten some of this out.
They shrink to the size of a plum, but they don’t collaps. Free divers learn to stretch their diaphragms to allow this, though it has little to do with fitness.
Due to pressure, water never gets colder than 4 degrees centigrade. Naturally, this would kill an unprotected diver in as many minutes, but temperature is not a factor of depth. I many waters these temperatures are encountered even in summer at 10m depth.
Nitrogen narcosis is only a factor if you’re breathing a gas at ambient pressure, and don’t compensate by modifying the mixture. For free divers, narcosis is not a factor.