Normoblast

NORMOBLAST (more correctly "nomoblast"), one of the types of nucleated red blood cells (erythroblasts) with a size on average equal to a normal erythrocyte [see separate table (Vol. I, art. 287-288), fig. 5]. In the series of red blood cells, the normoblast represents an intermediate stage between a normal erythrocyte and a proerythroblast (see Hematopoiesis). The normoblast has a mostly round, darkly staining nucleus with coarse (unlike the megaloblast) chromatin crossbars, running radially from the center to the periphery like spokes in a wheel. The hemoglobin-containing protoplasm of the normoblast stains either with acid aniline dyes (orthochromatic normoblast), or simultaneously with both acid and basic dyes (polychromatophilic normoblast), or predominantly with the latter (basophilic normoblast—the normoblast closest to the proerythroblast). In a normal human, normoblasts are present only in the bone marrow: in children—in both long tubular and short flat bones, in adults—only in the latter. In peripheral blood, normoblasts are encountered under normal conditions only in newborns, but under pathological conditions they may appear during anemias of various origins, reaching especially large quantities (normoblastosis)—during increased blood regeneration due to acute, significant blood loss, during increased acute breakdown of erythrocytes without suppression of the function of hematopoietic organs (see Hemolysis, hematolysis), and during irritation of the bone marrow due to widespread cancerous metastases in the bones. In all these cases, the quantity of normoblasts increases in the bone marrow as well. Upon the appearance of foci of extramedullary hematopoiesis (see), normoblasts appear in these as well. With the sudden appearance of large quantities of nucleated erythrocytes in the peripheral blood, as is sometimes observed in pernicious anemia, one speaks of a blood crisis (see); it is usually considered a harbinger of an impending remission. The absence of normoblasts in the peripheral blood during severe anemias is prognostically unfavorable, as it indicates a decrease in the regenerative function of the hematopoietic organs (the so-called aplastic form of anemia). In unstained preparations, normoblasts are recognized only with difficulty by the yellow-green color of their protoplasm; finding them requires staining of a dry preparation.