A Physiologist Writes
There’s a BIG difference in simulating individual organs and an individual. The organs cross talk and are talked to by the hypothalamus, the adrenal glands, the sympathetic, parasympathetic and somatic nervous systems etc. etc etc. The kidneys play a big role inn blood pressure regulation, both for self preservation (not enough blood the kidneys die) and as an evolved blood pressure regulation system. Simulate an isolated kidney and you don’t get that.
The integration of the organs into the whole is fiendishly complex, ask your friendly neighbourhood ER doctor who has to deal with sick people with multiple issues on a cocktail of treatments. Push them a little bit in the wrong direction and their systems can shut down.
When you are brain dead the heart still beats, respiration may not need to be supplemented. Back in the undergraduate teaching labs we used cane toads (in NZ imported from Fiji). If you pith a cane toad (mash the brain stem and upper spinal cord) you can open the chest and rig the heart up for measurement and it will beat and if you keep the skin wet the frog can respire. You can keep it going all day if you are researching so a 3hr lab is no problem. But the animal cannot be reanimated.
BTW to an nascent animal rightists we would reply that these are cane toads, vermin. NZ kids know about vermin and conservation ethos trumps animal rights. NZ lethally traps and poisons brush tailed possums (eat birds eggs, nestlings and trees), rats (birds, eggs, insects), stoats (birds, not enough of the rabbits) and sundry others. There’s a national program to rid the country of these. Feral cats are shot on sight. At some point when the others are gone cat ownership will have to be closely regulated and breeding licensed and controlled. We can’t let cats take over from the others.