The brain certainly needs a more constant and better regulated blood supply than any other of the body. The blood flow through a human brain weighing 1400 g (approximately 2% of the body weight) is about 750 ml/min, i.e., approximately 15–20% of all blood expelled by the heart into the systemic circulation passes through the brain per minute . In 1 min the brain utilizes on the average 49 ml of oxygen, i.e., about 20% of the total quantity utilized by all tissues of the body , and 76 ml glucose, i.e., 70% of all the glucose issuing from the liver . Under normal conditions the principal source of energy needed for neuron function is oxidation of glucose. However, the brain has no reserve of carbohydrates, and still less of oxygen, so that its normal metabolism depends entirely on a constant supply of blood-borne energy-giving materials. If the circulation stops, severe metabolic disturbances at once arise in the brain.
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