Regional blood flow

The control of blood flow to regions varies. There are four arteries that deliver almost all the blood to the brain: bilateral internal carotid and vertebral arteries. Blood PCO₂ is tightly regulated by the respiratory system and normally remains constant even during mild to moderate exercise. The constant blood PCO₂and autoregulation result in mostly constant brain blood flow. Diffusion between blood and the brain interstitium is very limited in most of the brain tissue. Astrocytes, surround the cerebral blood vessels and play a role in limiting diffusion between the brain interstitium and blood. The amount of coronary blood flow is determined primarily by local metabolic control. Control of coronary blood flow related to endothelial vasoactive factors is important. Changes in coronary blood vessel endothelial cell function are proving to be important in understanding coronary heart disease. As pulmonary blood flow increases, pressure increases within the pulmonary blood vessels.