About 18% of the total blood volume in the body circulates in the brain, accounting for about 2% of the body weight.
The brain receives blood from two pairs of large vessels: the internal carotid arteries, which arise from arteries in the neck, and the vertebral arteries, which arise from arteries in the chest. The vertebral arterial system supplies the brainstem, the cerebellum, the occipital lobe of the cerebrum, and parts of the thalamus, while the carotid arteries supply the rest of the forebrain. The cerebral vasculature transports oxygen, nutrients and other important substances to the brain to ensure its proper functioning.
The brain uses about 20% of the oxygen absorbed by the lungs. Maintaining a constant blood supply to the brain is essential for normal brain function. Brain tissue deprived of oxygen for less than 1 minute can result in loss of consciousness, and after approximately 5 minutes of blood deprivation, brain tissue is at risk of becoming permanently damaged.