EM 159 Platelet

Red Blood Cells

Transmission electron micrograph (TEM) of red blood cells (erythrocytes).

A red blood cell (red) is a biconcave (i.e., dumbbell) disc (~7.8 µm diameter) as seen in this section through its middle.

• Plasma Membrane - network of deformable cytoskeletal proteins bound to the interior of the plasma membrane.
• Nucleus - absent in mature (human) red blood cells. Extruded during development (erythropoiesis).
• Organelles - absent in mature red blood cells.
  • Use anaerobic glycolysis as an energy source because of the absence of mitochondria.
• Cytoplasm - contains a high concentration of hemoglobin and a limited number of enzymes for cell maintenance.
  • Uniform granular appearance of high electron density due to the iron atoms in hemoglobin.

Reticulocytes are immature red blood cells without a nucleus but contain some ribosomes, mitochondria, and granules. (Typically, 1 to 2% of circulating red blood cells.)

A platelet (green) is also visible.