The main difference between arterial and venous blood is that the oxygen content is different and the amount of carbon dioxide is also different, so the color is different. Generally arterial blood has higher oxygen content and lower carbon dioxide content, so the blood is bright red, while venous blood generally has lower oxygen content and higher carbon dioxide content, so the venous blood is dark red, but not the arterial blood flows in the arteries and the venous blood flows in the veins, for the body circulation, the arterial blood flows in the arteries, while for the pulmonary circulation, the venous blood flows in the pulmonary arteries and the pulmonary veins. This is the difference between arterial and venous blood, which is mainly determined by the amount of oxygen and carbon dioxide in the blood.