As ~blood~ travels through the body delivering oxygen and nutrients to the tissue, it also picks up carbon dioxide and other waste materials produced by the cells. This oxygen-poor ~blood~ is transported through a network of |veins| to the vena cava and to the right side of the |heart|, where it is then pumped into the |lungs|. The ~blood~ returning from the |veins| enters the right atrium of the |heart|, passes through the |tricuspid valve| to the right ~ventricle~, passes by the semilunar |valves| of the |pulmonary artery|, and goes to the |lungs| where carbon dioxide is exhaled and the ~blood~ is replenished with oxygen. The oxygen rich ~blood~ returning from the |lungs| enters the left atrium, passes the |mitral valve|, then enters the left ~ventricle~. From the left ~ventricle~ it is propelled past the semilunar |valves| of the |aorta| into the |aorta| itself and distributed through the body via a network of arteries.
