Why can't all cells preform all functions

We're doing gene regulation in bio and i was wondering why all cells cant preform all functions. If all cells contain the coding to preform all the functions why arent they all expressed? Why is it a liver cell is limited to ONLY being a liver cell. If all of the functions were expressed at once what would happen? Better yet why cant we grow back organs via stem cells, and i dont mean the transplanted ones from abortion i mean our actual own stem cells. If it's because our body just doesnt produce them after maturation okay but it seems like a simple task to induce production of them via drugs or possibly genetic engineering. Why is the distinction of a "liver" being a liver necessary why cant it just be an organ that preforms many functions including those of kidneys/intestines/heart. Aside from the spatial problems that arise i mean i'm talking pure function


Kinda alot of questions sorry but im sick of studying and i figure if im going to procrastinate ill do it in a productive way on yahoo. Thanks for the answers in advance as always

if all cells could preform all functions we would be dead, for instance the receptors to react to a specific hormone. Ill use an extreme example, when we reach puberty our pituitary gland sends out the hormone FSH in men to produce sperm. You kknow that sperm cells are haploid cells because of meiosis. There is a specific signal that tells these cells to undergo meiosis instead of mitosis. An hormones are spread throuout the body only and should only affect certain cells. Now if every cell carried out every function, by the time you were 12 all the cells in your body would be haploid, and thus youd be dead.
Another simple reason is it would be very costly energy wise, for every cell to preform every function.

Thanks to 549385 also! your answer was really thorough too but it came in JUST as i picked best answer. Sorry, thanks though still!

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