Oxygen-poor blood enters the heart through the right atrium. From there blood flows through the tricuspid valve into the right ventricle. When the heart contracts during the diastolic phase, this blood is pumped out through the pulmonary arteries that run toward the lungs. At the lungs, the blood is circulated through a series of progressively smaller arterioles until it flows through capillaries lining the lungs' alveolar sacs. It is here that gas exchange takes place as oxygen is taken up by the blood, and carbon dioxide is released into the waste air.After oxygenation, the fresh blood is circulated back through the bronchial veins and into the pulmonary veins. These run from the lungs and drain into the heart's left atrium. During the systolic phase of the heartbeat, the mitral valve under the left atrium opens and permits blood to pass into the left ventricle. This chamber is heavily muscled and it has the power to pump the oxygen-rich blood out through the aorta and into the rest of the body.
The circulatory and respiratory systems work together by the person breathing. They are actually connected because the respiratory system is because its the lungs. The lungs provide air for the for the body. The circulatory system is were the heart is placed. When the body breaths in air it expands the lungs and takes out co2, once the lungs expand it pumps the heart to keep pumping blood to the body which provides everything else in the body. If the heart doesn't have air/blood going thru it its starts to panic and die slowly.
