Schematic diagram of blood circulation of human heart

Blood flows from the right atrium into the right ventricle, from the right ventricle into the pulmonary artery, and then into the lungs to complete gas exchange. Blood enters the left atrium from the lung, then flows into the left ventricle from the left atrium, and then ejects blood from the left ventricle to reach the aorta, enters all organs of the body, and flows into the right atrium from all organs after gas exchange is completed, and so on.

Blood flows in the heart:

Superior and inferior vena cava → right atrium → right ventricle → pulmonary artery

Pulmonary vein → left atrium → left ventricle → aorta.

Blood circulation: whole body tissue cells

Oxygen = carbon dioxide

Systemic circulation: left ventricle → aorta → arteries at all levels → systemic capillaries → veins at all levels → superior and inferior vena cava → right atrium.

Pulmonary circulation: right ventricle → pulmonary artery → pulmonary capillary → pulmonary vein → left atrium.

Oxygen = carbon dioxide

pulmonary alveolus