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

red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

that contains a cell nucleus. Almost all

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...

organisms have

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyt ...

-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 to mature red blood cells in

erythropoiesis Erythropoiesis (from Greek 'erythro' meaning "red" and 'poiesis' "to make") is the process which produces red blood cells (erythrocytes), which is the development from erythropoietic stem cell to mature red blood cell. It is stimulated by decrea ...

, 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

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...

es 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 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 pl ...

peripheral blood smear A blood smear, peripheral blood smear or blood film is a thin layer of blood smeared on a glass microscope slide and then stained in such a way as to allow the various blood cells to be examined microscopically. Blood smears are examined in the ...

, 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-Pic ...

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 Primary myelofibrosis (PMF) is a rare bone marrow blood cancer. It is classified by the World Health Organization (WHO) as a type of myeloproliferative neoplasm, a group of cancers in which there is growth of abnormal cells in the bone marrow. ...

, 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 vie ...

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 (

myeloma Multiple myeloma (MM), also known as plasma cell myeloma and simply myeloma, is a cancer of plasma cells, a type of white blood cell that normally produces antibodies. Often, no symptoms are noticed initially. As it progresses, bone pain, anemi ...

leukemia Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ...

lymphoma Lymphoma is a group of blood and lymph tumors that develop from lymphocytes (a type of white blood cell). In current usage the name usually refers to just the cancerous versions rather than all such tumours. Signs and symptoms may include enla ...

s), and in chronic

hypoxemia Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the bod ...

.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 In linguistics, a word sense is one of the meanings of a word. For example, a dictionary may have over 50 different senses of the word "play", each of these having a different meaning based on the context of the word's usage in a sentence, as ...

. 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 ...

. In the latter

sense A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system re ...

, 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 Pernicious anemia is a type of vitamin B12 deficiency anemia, a disease in which not enough red blood cells are produced due to the malabsorption of vitamin B12. Malabsorption in pernicious anemia results from the lack or loss of intrinsic fa ...

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 synth ...

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 In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...

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 ar ...

. 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. ...

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