The liquid part of blood is called plasma. Approximately 92 percent of plasma is water, and the remainder is composed of proteins, salt, sugar, fats, hormones and vitamins.
In addition to plasma, blood contains red and white blood cells and platelets. Almost half of the blood is made of red blood cells. Red blood cells are produced in the bone marrow. They transport oxygen and iron throughout the body. White blood cells and platelets make up less than 1 percent of blood. White blood cells help the immune system fight off diseases. Platelets are responsible for causing the blood to clot when the body experiences an injury.