blood

blood The red fluid in the body that contains white and red blood cells, platelets, proteins, and other elements. Blood is transported throughout the body by the circulatory system. Blood flows in two directions: away from the heart (arterial blood) and toward the heart (venous blood). Arterial blood has a high concentration of oxygen and nutrients for body tissues, and venous blood is the means by which carbon dioxide is transported to the lungs for removal from the body. See also blood cell.