Erythropoiesis
- The process of erythrocyte (red blood cell) development, which, in adults, primarily occurs in the spongy bone marrow.
- Takes place in red marrow of spongy bone, aka, trabecular or cancellous bone.
Stages:
Common myeloid progenitor cell*
Arises within the red bone marrow*
Colony-forming unit – erythroid cells (CFU-E)*
- EPO (hormone released from the kidneys) induces entry into the erythroid series.
Proerythroblast*
Has a large nucleus, so that only a basophilic rim of agranular cytoplasm can be seen.
Golgi apparatus appears as a white "ghost" in the histological sample; though not shown here, the proerythroblast has an abundance of RNA and ribosome content.
The nuclear chromatin is fine and granular, with 1 – 2 nucleoli.
Basophilic erythroblast*
Smaller (~8-16 µm)
Cytoplasm appears even darker, more basophilic, because the polyribosomes are active in hemoglobin (Hb) synthesis.
The nuclear chromatin begins to form clumps, which, against the lighter-staining surrounding matter, can create a so-called "checkerboard" pattern.
Polychromatophilic erythroblast*
Bluish-gray hue - the presence of hemoglobin increases and the cytoplasm becomes more acidophilic ("polychromatophilic" = cell contains both basophilic and acidophilic matter).
Nucleus decreases in size, and the chromatin condenses; "checkerboard" pattern becomes more visible.
Orthocromatic erythroblast*
More acidophilic (hence, it is also referred to as an acidophilic erythrobast), due to the high concentration of hemoglobin
Pyknotic nucleus: as the chromatin degenerates, the nucleus shrivels to form a dense basophilic mass
- In transition to the next stage, the nucleus is extruded from the cell.
Reticulocyte*
Light pink/blue staining
Has no nucleus
Basophilic remnants of the reticulum and other organelles can still be seen.
- Eventually, these remnants are also lost, and the mature erythrocyte stains red; however, upon close inspection, we can see that its biconcave center stains lighter – this is referred to as the central pallor.
Additional Information:
- As the erythropoid series progresses, the cells become smaller: the proerythroblast is approximately 15-20 micrometers in diameter; the erythrocyte is only 7-8.5 micrometers.
- Be aware that a great deal of intertextual variation in nomenclature exists; in this tutorial, we've used the nomenclature that reflects changes in cytoplasmic staining as it goes from basophilic (dark purple/blue) to acidophilic (bright pinkish).
- Be aware that many texts use "erythroblast" and "normoblast" interchangeably.
Images:
Mark Braun, MD. http://medsci.indiana.edu/c602web/602/c602web/virtual_nrml/nrml_lst_pad.htm
