Blood circulation. Illustration of the human bodys blood vessels, shown in a standing figure. Note the heart in the upper centre, with the blood vessels of the lungs on either side. Arteries, which carry oxygenrich blood from the heart to the body, are coloured red. Veins, which return deoxygenated blood to the heart, are blue. The average adult has about five litres of blood. At rest this volume of blood passes through the heart and around the body each minute.
