4.7 to 6.1 million (male), 4.2 to 5.4 million (female) erythrocytes: Red blood cells contain the blood 's hemoglobin and distribute oxygen. Mature red blood cells lack a nucleus and organelles in mammals. The red blood cells (together with endothelial vessel cells and other cells) are also marked by glycoproteins that define the different blood types. The proportion of blood occupied by red blood cells is referred to as the hematocrit, and is normally about 45 %. The combined surface area of all red blood cells of the human body would be roughly 2,000 times as great as the body 's exterior surface.
the percentage of red blood cells compared to blood volume is known as
hematocrit