Blood is an essential element in the human body that distributes nitrogen, oxygen and other nutrients to vital organs. Blood is composed of plasma and blood cells. Plasma contains proteins that assist in blood clotting during injury. About half of blood volume is made up of blood cells. Red blood cells carry oxygen to tissues and organs, white blood cells fight infections and platelets assist in blood clotting.
The American Red Cross collects approximately 15.7 million blood donations every year in the United States. About 1 pint, or 473 cubic centimeters, of blood is collected during the donation. According to the American Red Cross, one blood donation can save up to three lives, as red blood cells, platelets and plasma can be used individually from the blood.Learn more about Measurements