The composition of blood consists of various components, such as plasma, white blood cells, red blood cells and platelets. Plasma, which is the fluid component that contains the different blood cells and substances of whole blood, represents 55 percent of whole blood.
Blood plasma is approximately 90 percent water and contains substances, such as white and red blood cells, gases, platelets, proteins, enzymes, hormones, waste and electrolytes and nutrients. Whole blood also consists of approximately 45 percent of red blood cells, which are also called erythrocytes. The function of red blood cells is to transport oxygen remove carbon dioxide in the body.
White blood cells are important because their function is to defend the body against germs and pathogens that cause disease or infections, and platelets help with blood coagulation.