Where it starts!!
The circulatory system is a constant loop. Let's start in the lungs where the blood receives oxygen and then travels to the heart through the pulmonary vein and enters the left atrium. Once through the left atrium it is pumped into the the left ventricle and the into the aorta. The aorta branches off into arteries to carry blood to all parts of the body ending in capillaries. The blood starts its journey back to the heart through a capillary, which leads to a vein. The vein takes the blood back to the heart entering in the right atrium then to the right ventricle. It then travels through the pulmonary vein and back to the lungs where everything starts all over again. It takes about a minute for the circulation of the blood to be completed.