Blood volume is a term describing the amout of blood (including both red blood cells and plasma) in a person's circulatory system. Red blood cells (erythrocytes) are present in the blood and help carry oxygen to the rest of the cells in the body Blood is a circulating tissue composed of fluid plasma and cells (red blood cells, white blood cells, platelets). ... Human red blood cells Red blood cells are the most common type of blood cell and are the vertebrate bodys principal means of delivering oxygen to body tissues via the blood. ... Blood plasma is the liquid component of blood, in which the blood cells are suspended. ... It has been suggested that Circulation (physiology) be merged into this article or section. ...