The movement cycle of the erythrocyte (or red blood cell).

Surrounded by platelets (thrombocytes), various hormones, salts, some proteins and wastes, the red blood cell (erythrocyte) which is contained in plasma, becomes oxygenated in a capillary in the left lung. From here it is forced into one of the pulmonary veins, and transported into the left atrium, a thin-walled chamber which acts as a reservoir, which then contracts, squeezing out any blood which hasn't already passed along into the left ventricle. The left ventricle is …

…the atrium into the right ventricle, where it is slowly released into one of the pulmonary arteries. These arteries supply the de-oxygenated blood to the lungs, where it reaches branched out capillaries, which allow the blood to be thin enough to properly diffuse the carbon dioxide out and the oxygen in through the alveoli of the lungs. Once the blood cell has been re-oxygenated in the lung, it is ready to start the circuit again.