On the whole, oxygen is absolutely required for survival. Loss of oxygen to any part of the body is known as hypoxia. Total loss of oxygen results in anoxia.
Due to the susceptibility of the human brain to oxygen, humans can survive for only a short period of time without a supply of oxygen to the brain. In spite of the fact that the brain weighs only 5% of the body's weight, it consumes some 20% of all the oxygen intake. Oxygen is supplied to the brain by blood. It takes only about 8 to 10 seconds of loss of oxygen to the brain to make us lose consciousness. Loss of oxygen to the brain for a period of 4 to 6 minutes results in destruction of the brain cells. Extended periods of time results in brain damage and ultimately death.
The brain can survive for longer periods of time at lower temperatures. That is due to the fact that at lower temperatures the brain requires less oxygen for its survival. This fact is made of use in major surgeries and is known as induced hypothermia.
The other tissues of the body can survive for longer periods of time without oxygen, which make organ transplantation possible.
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