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one of the formed elements in the peripheral blood, constituting the great majority of the cells in the blood. (For immature forms see erythrocytic series.) In humans the normal mature erythrocyte is a biconcave disk without a nucleus, about 7.7 micrometers in diameter, consisting mainly of hemoglobin and a supporting framework called the stroma. Erythrocyte formation (erythropoiesis) takes place in the red bone marrow in the adult, and in the liver, spleen, and bone marrow of the fetus. It requires an ample supply of dietary elements such as iron, cobalt, copper, amino acids, and certain vitamins. Called also red cell or corpuscle and red blood cell or corpuscle

The functions of erythrocytes include transportation of oxygen and carbon dioxide. They owe their oxygen-carrying ability to hemoglobin, a combination of an iron-containing prosthetic group (heme) with a protein (globin). Hemoglobin attracts and forms a loose connection with free oxygen, and its presence enables blood to absorb some 60 times the amount of oxygen that the plasma by itself absorbs. Oxyhemoglobin is red, which gives oxygenated blood its red color. Erythrocytes are stored in the spleen, which acts as a reservoir for the blood system and discharges the cells into the blood as required. The spleen may discharge extra erythrocytes into the blood during emergencies such as hemorrhage or shock.

Erythrocytes also are important in the maintenance of a normal acid-base balance, and, since they help determine the viscosity of the blood, they also influence its specific gravity. Their average life span is 120 days. They are subjected to much wear and tear in circulation and eventually are removed by cells of the reticuloendothelial system, particularly in the liver, bone marrow, and spleen. In spite of this constant destruction and production of erythrocytes, the body maintains a fairly constant number, between 4 and 5 million per mm3 of blood in women and 5 to 6 million per mm3 in men. A decreased number constitutes one form of anemia.

Erythrocytes are destroyed whenever they are exposed to solutions that are not isotonic to blood plasma. If they are placed in a solution that is more dilute than plasma (distilled water for example) the cells will swell until osmotic pressure bursts the cell membrane. If they are placed in a solution more concentrated than plasma, the cells will lose water and shrivel or crenate. It is for this reason that solutions to be given intravenously must be isotonic to plasma.

Aged red cells are ingested by macrophages in the spleen and liver. The iron is transported by the plasma protein transferrin to the bone marrow, where it is incorporated into new red cells. The heme group is converted to bilirubin, a bile pigment secreted by the liver. About 180 million red blood cells are destroyed every minute. Since the number of cells in the blood remains more or less constant, this means that about 180 million red blood cells are manufactured every minute.

Determination of the red blood cell volume is usually done as a preliminary step in determination of the total blood volume. A radioactive substance, usually chromium, is used to “tag” cells of a sample of blood drawn from the patient. The sample is then reintroduced into the circulating blood and subsequent samples are taken to be evaluated for degree of radioactivity. The degree of dilution is used to calculate total blood volume.
The events in the life of erythrocytes. Nucleated red blood cell (RBC) precursors stimulated by erythropoietin form erythrocytes in the bone marrow. Normal synthesis of hemoglobin occurs only in the presence of nutrients, iron, vitamin B12, and folic acid. Mature RBCs are released into circulation. The old or defective RBCs are degraded in the spleen. Iron and globin are reutilized immediately. Bilirubin is released in bile into the intestine. From Damjanov, 1996.
erythrocyte protoporphyrin test EP test; a screening test for lead toxicity; erythrocyte protoporphyrin levels are determined by direct fluorometry of whole blood or fluorescence analysis of whole blood extracts. Levels will be increased in either lead poisoning or iron deficiency.
erythrocyte sedimentation rate the rate at which erythrocytes settle out of unclotted blood in one hour. The test is based on the fact that inflammatory processes cause an alteration in blood proteins, resulting in aggregation of the red cells, which makes them heavier and more likely to fall rapidly when placed in a special vertical test tube. Normal ranges vary according to the type of tube used, each type being of a different size. The most common methods and the normal range for each are: Wintrobe method, 0 to 6.5 mm per hour for men, 0 to 15 mm per hour for women; and Westergren method, 0 to 15 mm per hour for men, 0 to 20 mm per hour for women.ƒ

The erythrocyte sedimentation rate is often inconclusive and is not considered specific for any particular disorder. It is most often used as a gauge for determining the progress of an inflammatory disease such as rheumatic fever, rheumatoid arthritis, or a respiratory infection. The information provided by this test must be used in conjunction with results from other tests and clinical evaluations.


A mature red blood cell.
[erythro- + G. kytos, cell]


/eryth·ro·cyte/ (ĕ-rith´ro-sīt) red blood cell; corpuscle; one of the formed elements in peripheral blood. Normally, in humans, the mature form is a non-nucleated, yellowish, biconcave disk, containing hemoglobin and transporting oxygen. For immature forms, see erythrocytic series, under series.
basophilic erythrocyte  an abnormal erythrocyte that takes basic stains, as seen in basophilia.
hypochromic erythrocyte  one that contains less than normal concentration of hemoglobin and as a result appears paler than normal; it is usually also microcytic.
normochromic erythrocyte  one of normal color with a normal concentration of hemoglobin.
polychromatic erythrocyte , polychromatophilic erythrocyte one that, on staining, shows shades of blue combined with tinges of pink.
target erythrocyte  see under cell.


e·ryth′ro·cyt′ic (-sĭt′ĭk) adj.


Etymology: Gk, erythros + kytos, cell
mature red blood cell; a biconcave disk about 7 μm in diameter that contains hemoglobin confined within a lipoid membrane. It is the major cellular element of the circulating blood and transports oxygen as its principal function. The number of red blood cells per microliter of blood is 4.5 to 5.5 million in men and 4.2 to 4.8 million in women. The red blood cell count varies with age, activity, and environmental conditions. An erythrocyte normally survives for 110 to 120 days, when it is removed from the bloodstream and broken down by the reticuloendothelial system. New erythrocytes are produced at a rate of slightly more than 1% a day; thus a constant level is usually maintained. Acute blood loss, hemolytic anemia, or chronic oxygen deprivation may cause erythrocyte production to increase greatly. Erythrocytes originate in the marrow of the flat bones or at the end of long bones. Maturation proceeds from the pronormoblast to the basophilic polychromatophilic normoblast to the basophilic polychromatophilic normoblast, and orthochromic normoblast the final stage before the mature adult cell develops. Also called red blood cell (RBC), red cell, red corpuscle. Compare normoblast, reticulocyte. See also erythropoiesis, hemoglobin, red cell indexes.


A mature, non-nucleated cell averaging 7–8 µm in diameter, which is round or ovoid on peripheral smear, contains haemoglobin and has a zone of central pallor due to the cell’s biconcavity. Erythrocytes are normally confined to blood vessels (aorta, arteries, arterioles, capillaries, venules, veins, inferior vena cava and superior vena cava), the heart and pulmonary vasculature. Haemoglobin, the main erythrocyte protein, is tasked with transporting O2 to tissues and CO2 away from tissues. Erythrocytes have an average lifespan of 120 days.


RBC, red blood cell, discocyte Hematology A mature, nonnucleated cell averaging 7–8 µm in diameter, which is round or ovoid on peripheral smear, contains Hb and has a zone of central pallor due to the cell's biconcavity. See Fetal erythrocyte.


A mature red blood cell.
Synonym(s): hemacyte, red blood cell, red cell, red corpuscle.
[erythro- + G. kytos, cell]


(e-rith'ro-sit?) [ erythro- + -cyte]
Enlarge picture
ERYTHROCYTES: Note the different size and shape of the red blood cells
A blood cell (i.e., a circulating cell that contains hemoglobin and carries oxygen to tissue). Each erythrocyte is a nonnucleated, biconcave disk averaging 7.7 µm in diameter. An erythrocyte has a typical cell membrane and an internal stroma made of lipids and proteins to which more than 200 million molecules of hemoglobin are attached. The total surface area of the erythrocytes of an average adult is 3820 sq m, or about 2000 times more than the external total body surface area. Synonym: red blood cell; red blood corpuscle; red cell; red corpuscle See: illustration


In a normal person, the number of erythrocytes averages about 5,000,000/µL (5,500,000 for men and 4,500,000 for women). The total number in an average-sized person is about 35 trillion. The number per µL varies with age (higher in infants), time of day (lower during sleep), activity and environmental temperature (increasing with both), and altitude. People living at altitudes of 10,000 ft (3048 m) or more may have an erythrocyte count of 8,000,000/µL or more.

If a person has a normal blood volume of 5 L (70 mL/ kg of body weight) and 5,000,000 erythrocytes per µL of blood, and the erythrocytes live 120 days, the red bone marrow must produce 2,400,000 erythrocytes per second to maintain this erythrocyte count.


The primary function of erythrocytes is to carry oxygen. The hemoglobin also contributes to the acid-base balance of the blood by acting as a buffer for the transport of carbon dioxide in the plasma as bicarbonate ions.


Erythrocyte formation (erythropoiesis) in adults takes place in the bone marrow, principally in the vertebrae, ribs, sternum, hip bone, diploë of cranial bones, and proximal ends of the humerus and femur. erythrocytes arise from large nucleated stem cells (promegaloblasts), which give rise to pronormoblasts, in which hemoglobin appears. These become normoblasts, which extrude their nuclei. erythrocytes at this stage possess a fine reticular network and are known as reticulocytes. This reticular structure is usually lost before the cells enter circulation as mature erythrocytes. The proper formation of erythrocytes depends primarily on nutrition, with protein, iron, and copper essential for the formation of hemoglobin, and vitamin B12 and folic acid necessary for DNA synthesis in stem cells of the red bone marrow.

As erythrocytes age and become fragile, they are removed from circulation by macrophages in the liver, spleen, and red bone marrow. The protein and iron of hemoglobin are reused; iron may be stored in the liver until needed for the production of new erythrocytes in the bone marrow. The heme portion of the hemoglobin is converted to bilirubin, which is excreted in bile as one of the bile pigments.


On microscopic examination, erythrocytes may reveal variations in the following respects: size (anisocytosis), shape (poikilocytosis), staining reaction (achromia, hypochromia, hyperchromia, polychromatophilia), structure (possession of bodies such as Cabot's rings, Howell-Jolly bodies, Heinz bodies; parasites such as malaria; a reticular network; or nuclei), and number (anemia, polycythemia).

achromatic erythrocyte

An erythrocyte from which the hemoglobin has been dissolved; a colorless cell.

basophilic erythrocyte

An erythrocyte in which cytoplasm stains blue. The staining may be diffuse (material uniformly distributed) or punctate (material appearing as pinpoint dots).

crenated erythrocyte

An erythrocyte with a serrated or indented edge, usually the result of withdrawal of water from the cell, as occurs when cells are placed in hypertonic solutions.

immature erythrocyte

Any incompletely developed erythrocyte.

orthochromatic erythrocyte

An erythrocyte that stains with acid stains only, the cytoplasm appearing pink.

polychromatic erythrocyte

An erythrocyte that does not stain uniformly.


A red blood cell. ‘Erythro’ means ‘red’, and ‘cyte’ means ‘cell’. Erythrocytes are flattened discs, slightly hollowed on each side (biconcave) and about 7 thousandths of a millimetre in diameter. They contain HAEMOGLOBIN and their main function is to transport OXYGEN from the lungs to the tissues.
Erythrocyteclick for a larger image
Fig. 154 Erythrocyte . (a) Surface view. (b) Vertical section.

erythrocyte or red blood cell (RBC)

a vertebrate cell that contains HAEMOGLOBIN pigment for oxygen transport from lungs to tissues and carries small amounts of carbon dioxide as HCO3 - from tissues to lungs (see also CHLORIDE SHIFT). Unlike other vertebrate cells, mammalian RBCs are non-nucleated and have definite biconcave shape. Compare LEUCOCYTE.


Mentioned in: Hemolytic Anemia


red blood corpuscle; mature red blood cell


A mature red blood cell.
[erythro- + G. kytos, cell]

erythrocyte (ərith´rōsīt),

n a red blood cell; a nonnucleated, circular, biconcave, discoid, hemoglobin-containing, oxygen-carrying formed element circulating in the blood.
erythrocyte count,
n the number of red blood cells per cubic millimeter of blood.
erythrocyte indices, the standard values of red blood cell numbers, morphologic characteristics, and behavior in comprehensive hematologic laboratory testing.
erythrocyte sedimentation rate (ESR),
n the rate at which red blood cells settle in a pipette of unclotted blood, measured in millimeters per hour. It is used as an index of inflammation.


a red blood cell, or corpuscle; one of the formed elements in the peripheral blood. For immature forms see normoblast, metarubricyte. In most mammals mature erythrocytes are biconcave disks that have no nuclei. The degree of concavity varies between species, as does the size. Birds have nucleated, oval erythrocytes. The cell consists mainly of hemoglobin and a supporting framework, called the stroma. Erythrocyte formation (erythropoiesis) takes place in the red bone marrow in the adult, and in the liver, spleen and bone marrow of the fetus. Erythrocyte formation requires an ample supply of certain dietary elements such as iron, cobalt and copper, amino acids and certain vitamins.

erythrocyte antigen
see blood group antigen and blood group.
erythrocyte casts
see urinary cast.
erythrocyte count
erythrocyte ghosts
in new methylene blue, erythrocytes fail to take up stain and appear only as a pale outline.
hypochromatic erythrocyte
see hypochromia (2).
erythrocyte indices
calculated values for the mean corpuscular volume (mcv), mean corpuscular hemoglobin (mch), and mean corpuscular hemoglobin concentration (mchc), taken from the hematocrit, hemoglobin concentration and red blood cell count. Used in determining the likely etiology of anemias and other abnormalities of the erythron. Called also mean cell constants.
matchstick erythrocyte
describes the appearance of sickled deer erythrocytes containing hemoglobin II.
normochromic erythrocyte
erythrocyte refractile bodies (ERF)
a term usually used to describe Heinz bodies in the erythrocytes of cats. Sometimes restricted in definition to the smaller (Heinz) bodies that are normally found in up to 10% of feline erythrocytes, as distinct from larger bodies associated with hemolytic anemia.
erythrocyte sedimentation rate (ESR)
an expression of the extent of settling of erythrocytes in a column of fresh citrated or otherwise treated blood, per unit of time. Of greatest diagnostic value in dogs as horses normally have a greatly accelerated rate and ruminants show none except in very extreme circumstances. In the dog, ESR is elevated with inflammatory processes. See also sedimentation rate.
erythrocyte tonicity
the degree of distention of the erythrocyte. This is dependent on the osmotic pressure of the cell's contents compared with that of the plasma. If it is greater, water will pass into the cell and it may rupture. If it is less, water passes out of the cell which shrinks and becomes crenated.
erythrocyte volume
mean corpuscular volume (mcv); see erythrocyte indices (above).

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