Histology of the Erythroid Series Histology > Tissue Types > Tissue Types 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 Powered by TCPDF (www.tcpdf.org) 1 / 1.