Red blood cell Red blood cell Red blood cells, also known as RBCs, red cells, red blood corpuscles, haematids, erythroid cells or erythrocytes (from Greek "erythros" for "red" and "kytos" for "hollow vessel", with "-cyte" translated as "cell" in modern usage), are the most common type of blood cell and the vertebrate's principal means of delivering oxygen (O) to the body tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or gills of fish, and release it into tissues while squeezing through the body's capillaries. The cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can
Blood the presence of potential molecular fibers in the form of fibrinogen. Blood performs many important functions within the body, including: Blood accounts for 7% of the human body weight, with an average density around 1060 kg/m, very close to pure water's density of 1000 kg/m. The average adult has a blood volume of roughly , which is composed of plasma and several kinds of cells. These blood cells (which are also called corpuscles or "formed elements") consist of erythrocytes (red blood cells, RBCs), leukocytes (white blood cells), and thrombocytes (platelets). By volume, the red blood cells constitute about 45% of