 Systemic circulation is the portion of the cardiovascular system which transports oxygenated blood away from the heart through the aorta from the left ventricle where the blood has been previously deposited from pulmonary circulation, to the rest of the body, and returns oxygen-depleted blood back to the heart.The brain has a dual blood supply that comes from arteries at its front and back.These are called the "anterior" and "posterior" circulation respectively.