Life span:in blood, 8–12 hrin CT, 1–2 days • Difficult to Identify 55 hr • Nucleus large, slightly
Large, kidney-shaped •
Life span:in blood, 16 hr
Life span:in CT, unknown
Large,•euchromatc spherical nucleus;3–5 nucleoli
Increased size,
Life span:in blood, 8–12 hrin CT, unknown
Large,•euchromatic spherical nucleus; 3–5nucleoli • Increased size, 18–24 m • Last cell capable of mitosis
Life span:in blood, 8 hrin CT, unknown
This table summarizes the maturation of blood cells with histologic characteristics at the various stages, maturation time, and life span after leaving the marrow. Times indicated along vertical lines are the approximate time between recognizable stages. ↑M-1 wk indicates increase in number by mitosis for 1 week before differentiation begins; MEP, megakaryocyte/erythrocyte progenitor cell; MKP, megakaryocyte progenitor cell; BMCP, basophil/mast cell progenitor cell; ErP, erythrocyte progenitor cell; NoP, neutrophil progenitor cell; MoP, monocyte progenitor cell; BaP, basophil progenitor cell; CT, connective issue.
Figure 10.19. Figure 10.19 shows the stages of blood cell development in which characteristic cell types can be identified in the light microscope in a tissue section or bone marrow smear. Hemopoiesis is initiated in an apparently random manner when individual HSCs begin to differentiate into one of the lineage-restricted progenitor cells. Progenitor cells have surface receptors for specific cytokines and growth factors, including colony-stimulating factors
FIGURE 10.19 • Stages of erythrocytic and granular leukocytic differentiation with Romanovskytype stain. Shown here are normal human bone marrow cells as they basophil would typically appear in a smear.
(CSFs), that influence their proliferation and maturation into a specific lineage.
Development of Erythrocytes (Erythropoiesis)
Erythrocyte development starts from CMP cells that, under the influence of erythropoietin, IL-3, and IL-4, differentiate to MEP cells. Expression of transcription factor GATA-1is required for the terminal differentiation of MEP cells to definitive erythroid cell lineage. Under GATA-1 influence, MEP cells transform into erythropoietin-sensitive erythrocyte-committed progenitors (ErPs or CFU-E) that give rise to the proerythroblast.
The first microscopically recognizable precursor cell in erythropoiesis is called the proerythroblast.
The proerythroblast is a relatively large cell measuring 12 to 20 m in diameter. It contains a large spherical nucleus with one or two visible nucleoli. The cytoplasm shows mild basophilia because of the presence of free ribosomes. Although recognizable, the proerythroblast is not easily identified in routine bone marrow smears.
The basophilic erythroblast is smaller than the proerythroblast, from which it arises by mitotic division.
The nucleus of the basophilic erythroblast is smaller (10 to 16 m in diameter) and progressively more heterochromatic with repeated mitoses. The cytoplasm shows strong basophilia because of the large number of free ribosomes (polyribosomes) that synthesize hemoglobin. The accumulation of hemoglobin in the cell gradually changes the staining reaction of the cytoplasm so that it begins to stain with eosin. At the stage when the cytoplasm displays both acidophilia, because of the staining of hemoglobin, and basophilia, because of the staining of the ribosomes, the cell is called a polychromatophilic erythroblast.