Notes
Histology of the Erythroid Series
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Erythropoiesis Overview
Erythropoiesis is 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 of Erythropoiesis
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
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.
Erythrocyte
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.
Image credits
Mark Braun, MD. http://medsci.indiana.edu/c602web/602/c602web/virtual_nrml/nrml_lst_pad.htm