Abstract animation video of a blood clot. Blood is a specialized bodily fluid that delivers necessary substances to the body's cells – such as nutrients and oxygen – and transports waste products away from those same cells. About 55% of blood is blood plasma, a fluid that is the blood's liquid medium. Blood cells include erythrocytes which are red blood cells, leukocyte which are white blood cells and hrombocytes which are platelets. These blood cells make up to 45% of blood tissue, the remaining 55% is composed of plasma, the liquid component of blood. A blood clot blocks the flow of blood in an artery or vein in a human body. Free medical stock videos from animation company Polymime.