1. The fluid consisting of plasma, red blood cells, white blood cells, and platelets that is circulated by the heart through the arteries and veins, carrying oxygen and nutrients to and waste materials away from all body tissues. 2.lood varies in color from a bright red in the arteries to a duller red in the veins. The total quantity of blood within an individual depends upon body weight; a person weighing 70 kg (154 lb) has about 4.5 liters of blood in the body.