The amount of blood produced in the body between 5 - 6 liters and pump this amount through the heart too many times a day, about 20% of the amount of blood pumped by the heart every time you go to the brain, bringing the amount of blood passing by the brain every day as large as 1000 liters
An adults brain requires around 20% of the body's oxygen. Approximately 20% of the blood flowing from the heart is pumped to the brain. The brain needs constant blood flow in order to keep up with the heavy metabolic demands of the neurons.