Nucleated red blood cell

Several names are used for nucleated RBCs—erythroblast, normoblast, and megaloblast—with one minor variation in word sense. The name normoblast always refers to normal, healthy cells that are the immediate precursors of normal, healthy, mature (anucleate) RBCs. The name megaloblast always refers to abnormally developed precursors. Often the name erythroblast is used synonymously with normoblast, but at other times it is considered a hypernym. In the latter sense, there are two types of erythroblasts: normoblasts as cells that develop as expected, and megaloblasts as unusually large erythroblasts that are associated with illness. ==Healthy development==

There are four stages in the normal development of a normoblast. ==Pathogenesis==

A megaloblast is an unusually large erythroblast that can be associated with vitamin B12 deficiency (caused by pernicious anemia or dietary insufficiency), folic acid deficiency, or both (such anemias are collectively called megaloblastic anemias). This kind of anemia leads to macrocytes (abnormally large red cells) and the condition called macrocytosis. The cause of this cellular gigantism is an impairment in DNA replication that delays nuclear maturation and cell division. Because RNA and cytoplasmic elements are synthesized at a constant rate despite the cells' impaired DNA synthesis, the cells show nuclear-cytoplasmic asynchrony. ==Additional images==

Image:Illu blood cell lineage.jpg|Blood cell lineage Image:Hematopoiesis (human) diagram en.svg|Hematopoiesis ==See also==