A nucleated red blood cell (NRBC), also known by several other names, is a red blood cell that contains a

cell nucleus The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, h ...

. Almost all vertebrate organisms have hemoglobin-containing cells in their blood, and with the exception of mammals, all of these red blood cells are nucleated. In mammals, NRBCs occur in normal development as

precursors Precursor or Precursors may refer to: *Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of unr ...

to mature red blood cells in erythropoiesis, the process by which the body produces red blood cells. NRBCs are normally found in the bone marrow of humans of all ages and in the blood of fetuses and newborn infants. After infancy, RBCs normally contain a nucleus only during the very early stages of the cell's life, and the nucleus is ejected as a normal part of

cellular differentiation Cellular differentiation is the process in which a stem cell alters from one type to a differentiated one. Usually, the cell changes to a more specialized type. Differentiation happens multiple times during the development of a multicellular ...

before the cell is released into the bloodstream. Thus, if NRBCs are identified on an adult's

complete blood count A complete blood count (CBC), also known as a full blood count (FBC), is a set of medical laboratory tests that provide information about the cells in a person's blood. The CBC indicates the counts of white blood cells, red blood cells and pla ...

or peripheral blood smear, it suggests that there is a very high demand for the bone marrow to produce RBCs, and immature RBCs are being released into circulation. Possible

pathologic ''Pathologic'' ( rus, Мор. Утопия, Mor. Utopiya, ˈmor ʊˈtopʲɪjə, , More. Utopia – a pun on Thomas More's ''Utopia'' and the Russian word for "plague") is a 2005 role-playing and survival game developed by Russian studio Ice-P ...

causes include

anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, t ...

, myelofibrosis, thalassemia,

miliary tuberculosis To disseminate (from lat. ''disseminare'' "scattering seeds"), in the field of communication, is to broadcast a message to the public without direct feedback from the audience. Meaning Dissemination takes on the theory of the traditional view ...

cancers Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...

involving bone marrow ( myelomas, leukemias, lymphomas), and in chronic hypoxemia.Blood Smear: Details on RBCs, WBCs
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Nomenclature

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 linguistics, semantics, general semantics, and ontologies, hyponymy () is a semantic relation between a hyponym denoting a subtype and a hypernym or hyperonym (sometimes called umbrella term or blanket term) denoting a supertype. In other wor ...

. 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 Folate deficiency, also known as vitamin B9 deficiency, is a low level of folate and derivatives in the body. Signs of folate deficiency are often subtle. A low number of red blood cells (anemia) is a late finding in folate deficiency and folate ...

, or both (such

s are collectively called

megaloblastic anemia Megaloblastic anemia is a type of macrocytic anemia. An anemia is a red blood cell defect that can lead to an undersupply of oxygen. Megaloblastic anemia results from inhibition of DNA synthesis during red blood cell production. When DNA synthes ...

s). This kind of anemia leads to macrocytes (abnormally large red cells) and the condition called

macrocytosis Macrocytosis is the enlargement of red blood cells with near-constant hemoglobin concentration, and is defined by a mean corpuscular volume (MCV) of greater than 100 femtolitres (the precise criterion varies between laboratories). The enlarged er ...

. The cause of this cellular gigantism is an impairment in DNA replication that delays nuclear maturation and

cell division Cell division is the process by which a parent cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukaryotes, there a ...

. Because RNA and

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. Th ...

ic 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

References

External links