The mature human erythrocyte measures about 7-8 um in diameter and appears as an anucleate, acidophilic body. In addition to the nucleus, the mature erythrocyte also loses Golgi apparatus, centrioles, ER and most of its mitochondria. Few organelles present. A biconcave disk to achieve a maximum surface area to cytoplasmic volume ratio. The cell is enclosed in a typical fluid, bilayered cell membrane which is flexible and elastic enough to allow the cell to move through capillaries.
Cells frequently assume a cup shape in capillaries.
Peripheral membrane proteins, spectrin and actin, serve a cytoskeletal function. As red blood cells age, the surface area decreases relative to cytoplasmic volume resulting in a sphere form which is more rigid and is ultimately trapped in splenic cords. To provide an environment for the iron containing respiratory pigment, heme, which is complexed to two alpha and two beta globulin chains comprising the hemoglobin molecule. The erythrocyte also contains enzymes which participate in the glycolytic and hexose monophosphate biochemical pathways. These are less mature erythrocytes.