How long can we survive without oxygen?

 How long can we survive without oxygen?

 Humans can survive only for a few minutes without oxygen.This is because of the susceptibility of the brain cells. Even though the brain is only about 2 percent of the body's weight,it consumes about 20 percent of the oxygen we breathe in.

 Hence if oxygen supplied by the blood is stopped for a fee minutes,the brain ceases its function resulting ind death.We will lose consciousness in 8-10 seconds after the blood supply to the brain is cut.

 Brain cells can survive for long periods without oxygen at very low temperatures,as oxygen consumption is reduced.This technique,induced hypothermia,is made used of during major surgeries.Other tissues can survive for long periods without oxygen and that is why it is possible to remove organs,from brain dead persons for transplantation.