The systemic and pulmonary circuits are crucial components of the circulatory system, working together to transport blood between the heart, lungs, and the rest of the body. The process begins with pulmonary circulation, where deoxygenated blood is pumped from the right ventricle to the lungs via the pulmonary trunk and arteries. Upon reaching the lungs, the blood becomes oxygenated and returns to the heart, specifically to the left atrium, via the pulmonary veins.

The oxygenated blood is sent from the left atrium to the left ventricle, marking the start of systemic circulation. This circuit transports blood from the heart to all parts of the body. As the blood leaves the left ventricle, it enters the ascending aorta, passes through the aortic arch, and is carried by the descending aorta to various tissues throughout the body.

During this journey, the blood exchanges gases and nutrients with the surrounding tissues, becoming deoxygenated in the process. This deoxygenated blood makes its way back to the heart, entering the right atrium via systemic veins. These include the superior vena cava, which carries blood from above the diaphragm; the inferior vena cava, which carries blood from below the diaphragm; and the coronary sinus, which carries blood from the myocardium. From the right atrium, the blood is pumped to the right ventricle, repeating the cycle of pulmonary circulation.