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. …
