The heart is a large muscular organ which constantly pushes oxygen-rich blood to the brain and extremities and transports oxygen-poor blood from the brain and extremities to the lungs to gain oxygen. Blood comes into the right atrium from the body, moves into the right ventricle and is pushed into the pulmonary arteries in the lungs. After picking up oxygen, the blood travels back to the heart through the pulmonary veins into the left atrium, to the left ventricle and out to the body's tissues through the aorta.*

 

On average, your body has about 5 liters of blood continually circulating through it by way of the circulatory system. The heart, the lungs, and the blood vessels work together to form the circle part of the circulatory system.*

 

The pumping of the heart forces the blood on its journey. The body's circulatory system really has three distinct parts: pulmonary circulation, coronary circulation, and systemic circulation. Or, the lungs (pulmonary), the heart (coronary), and the rest of the system (systemic).*

 

Source: U.S. National Library of Medicine 

----------