RT Book, Section A1 Mohandas, Narla A2 Kaushansky, Kenneth A2 Prchal, Josef T. A2 Burns, Linda J. A2 Lichtman, Marshall A. A2 Levi, Marcel A2 Linch, David C. SR Print(0) ID 1180479226 T1 Structure and Composition of the Erythrocyte T2 Williams Hematology, 10e YR 2021 FD 2021 PB McGraw-Hill Education PP New York, NY SN 9781260464122 LK hemonc.mhmedical.com/content.aspx?aid=1180479226 RD 2024/03/28 AB SUMMARYCollectively, the erythroid progenitors, terminally differentiating erythroblasts (precursors), and adult red cells are termed the erythron to reinforce the idea that they function as an organ*. The widely dispersed cells comprising this organ arise from pluripotential hematopoietic stem cells. Following commitment to the erythroid lineage (unipotential progenitor), further maturation gives rise to the erythroid progenitors, burst-forming unit–erythroid and, subsequently, colony-forming unit–erythroid (CFU-E), that can be identified by their development into representative clonal colonies of red cells in vitro. The CFU-E then undergoes terminal differentiation, progressing through four to five morphologic stages, each having characteristic light microscopic and ultrastructural features. During terminal erythroid differentiation, there is an increasing amount of hemoglobin synthesis accompanied by nuclear chromatin condensation and at the final stage of differentiation, there is nuclear extrusion to generate an anucleate polychromatophilic macrocyte (reticulocyte with supravital staining). The human polychromatophilic macrocyte (reticulocyte) matures over 2 to 3 days, first in the marrow and then in circulation into the discoid erythrocyte. During reticulocyte maturation, cytoplasmic inclusions, including residual mitochondria and ribosomes, are degraded and the reticulocyte loses surface area to achieve the mean cell volume and surface area of a discoidal erythrocyte. Mature erythrocytes are approximately 7 to 8 μm in diameter and undergo extensive deformation to pass through 3-μm-diameter capillaries and the 1-μm-wide and 0.5-μm-thick endothelial slits in the red pulp of the spleen. The ability of the red cell to undergo extensive reversible deformation is essential for both its function and its survival. Red cell deformability is a function of its geometry, the viscosity of the cytoplasm, largely determined by the concentration of hemoglobin. Decreased deformability is a feature of red cells in various pathologic states. The erythrocyte is unique among eukaryotic cells in that its principal physical structure is its cell membrane, which encloses a concentrated hemoglobin solution. Thus, all structural properties of this cell are in some way linked to the cell membrane. In contrast to other cells, the erythrocyte has no cytoplasmic structures or organelles. Among human cells, only red cells and platelets do not have a nucleus.