Composition of the blood In the adult, the average amount of blood is 5 liters or approximately 7.7% of the body weight. The blood plasma comprises approximately 55% of the blood. It is almost clear, a straw-colored fluid of which approximately 90% is water. arterial blood: bright red = oxyhemoglobin venous blood: darker red

Composition: plasma 55% of volume formed elements 45% =RBC’s, WBC’s, Platelets