MEGALOBLAST

MEGALOBLAST (from Greek megas- large and blastos- bud), according to Ehrlich, nucleated immature red blood cells, significantly larger (10-20 μ) than normal erythrocytes. When particularly large, these cells are called megaloblasts. The most characteristic feature of a young megaloblast is a large nucleus with an extremely delicate reticular structure and more or less pronounced basophilia of the cytoplasm. More mature forms have a pyknotic peripherally located nucleus and abundant cytoplasm. Sometimes, in megaloblasts, disintegration of the nucleus into separate clumps (karyorrhexis) and figures of karyokinetic division of the nucleus are observed. When the nucleus is significantly pyknotic, it is difficult to distinguish a megaloblast from a macroblast (see also Hematopoiesis, hematopoietic organs-erythropoiesis). The distinguishing features are the more delicate structure of the nucleus and the greater richness of hemoglobin in the young megaloblast compared to the macroblast. Megaloblasts are characteristic of embryonic blood; in post-fetal life, they are encountered particularly frequently in pernicious anemia (megaloblastic reaction of the bone marrow). The presence of megaloblasts in peripheral blood is characteristic of macrocytic anemias. Besides pernicious anemia, megaloblastosis also occurs in some cases of carcinomatosis of the bone marrow, hemolytic jaundice, anemias based on pregnancy, childhood anemias, in carriers of the broad tapeworm, sometimes in malaria, syphilis (Timofeevsky). The appearance of megaloblasts in peripheral blood indicates a pathological regenerative function of the bone marrow (see Hematopoiesis, hematopoietic organs).