Erythrocytes . Also called red blood cells or red blood cells, they are the most numerous formed elements ( cells ) of the blood (around 5 000 000 per mm³), which have a fairly uniform size (diameter of about 7.5 µm) and the shape of biconcave discs, for which when observed under a microscope shows a clearer central area. They receive their name because in large quantities they give the blood a red color, although when observed in isolation in fresh blood (unstained) preparations, they present a greenish-yellow color.
Summary
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- 1 Etymology
- 2 Morphofunctional characteristics
- 3 Characterization
- 4 Erythrocytosis
- 5 Physical properties
- 6 Osmotic balance
- 7 Rh antigenic system
- 8 Erythrocyte formation
- 9 Half-life
- 10 External links
- 11 Sources
Etymology
The name erythrocyte derives from the combination of the ancient Greek words (ερυΘρος – erythrós ): “red”, and (κϒθος – kytos ): “cell”
Morphofunctional characteristics
Image of a red blood cell.
The cytoplasmic membrane of the red blood cell is associated with the cytoskeleton , made up of proteins such as spectrin , ancrine, and band 3 , among others. The function of this protein framework determines the shape of the red blood cell, but allows its necessary deformation when passing through very narrow capillaries, in which the erythrocyte adopts ellipsoidal conformations and other varieties. The sphingolipids present in the membrane constitute the antigens for the blood groups of the ABO system . The cytoplasm has an affinity for acid dyes ( eosin) with which it acquires a pink hue due to the presence of hemoglobin . They are cells that do not have nuclei, mitochondria , lysosomes , ribosomes , endoplasmic reticulum and the Golgi apparatus . This makes your metabolism very limited. Although it is true that it requires a lesser amount of energy than other cells, it needs it and its reducing capacity for different processes.
Most of the ATP is consumed in the maintenance of low concentrations of Na + and Ca +2 and high K + inside the cell, against the concentration gradient. On the other hand, the reducing potential is required to maintain the Fe +2 of hemoglobin in its functional state, the SH groups of hemoglobin and other proteins in the reduced state, essential to maintain the integrity of the cell membrane and the cytoskeleton.
Characterization
Erythrocytes are characterized in that their fundamental content is hemoglobin, which gives the erythrocyte its characteristic color and the function of transporting oxygen from the lungs to the tissues, and part of the carbon dioxide from the tissues to the lungs, participates in this way in the breathing process. Furthermore, like all proteins , it contributes to maintaining the acid-base balance of the blood by acting as a buffering system for blood pH (buffer system).
Variations of erythrocytes in terms of their number ( erythrocytosis : “increase” and erythropenia : “decrease”), size ( anisocytosis : “size difference”), shape ( poikilocytosis : “different forms”) and content occur in certain disease states. of hemoglobin (hypochromic: “low content” and hyperchromic: “high content”).
Erythrocytosis
Erythrocytosis is a disorder observed in polycythemia , while in anemias different alterations of erythrocytes can occur, mainly in their size and hemoglobin content (corpuscular constants), which serve as the basis for the morphological classification of anemias:
- Normochromic normocytic (from hemorrhage and hemolysis)
- Hypochromic microcytic (due to irondeficiency )
- Macrocytic (due to deficiency of vitamin B12and folic acid )
Physical properties
Among the physical properties of erythrocytes can be mentioned:
- Its elasticity.
- Tendency to adhere.
- Globular resistance.
- Antigenic function.
These cells have great elasticity, so they can pass through small-gauge blood capillaries. In slow circulation and in fresh blood preparations that are kept at rest they tend to adhere to each other and form columns similar to coin stacks , due to the superficial tension of their membrane .
Sedimentation: erythrocytes are the components of the blood with the highest density, therefore, when blood is drawn and placed in a glass tube with any anticoagulant ( heparin ), when it is kept at rest or centrifuged, the erythrocytes sediment. Based on this property, 2 tests of clinical interest are performed: erythrocyte sedimentation that determines the sedimentation rate of erythrocytes (-20 mm / h) and the hematocrit to calculate the relative volume of these cells with blood plasma (40-50 V %).
Red cell adenosine deaminase .
Osmotic balance
Under normal conditions there is an osmotic balance between the content of erythrocytes and plasma. If the plasma concentration increases (hypertonic), the water leaves the erythrocytes and retracts, reason why they present a jagged surface (creation). If the plasma concentration decreases (hypotonic), the water penetrates the erythrocytes and swells, so they acquire a spherical shape, until they disintegrate and the hemoglobin dissolves in the plasma ( hemolysis ). The globular resistance or the ability of the red blood cell to retain hemoglobin when placed in hypotonic solutions, can be measured by the osmotic fragility test of red blood cells, which is useful in the diagnosis of hemolytic anemias.
Rh antigenic system
The Rh antigenic system receives this name because it normally exists in the erythrocytes of the Macacos rhesus monkey and is present in most people, approximately 85% (Rh positive), while a minority lacks it (Rh negative).
The importance of this antigenic system lies in the danger of performing blood transfusions, in which the donor’s blood is Rh positive and that of the Rh negative recipient, because in the latter, antibodies ( anti Rh agglutinins ) are slowly developed during the following weeks , and the individual is “sensitized”, therefore, if the transfusion is repeated afterwards, this causes agglutination and hemolysis of the erythrocytes, which can be extremely serious. This hemolytic reaction also occurs in fetal erythroblastosis , a disease of the newborn, which generally occurs when the mother is Rh negative and develops antibodies against the Rh positive fetus .
Erythrocyte formation
Erythrocytes are derived from compromised stem cells called erythrotoblasts found in the bone marrow . The renal hormone erythropoietin stimulates erythropoiesis (erythrocyte formation) and is responsible for maintaining a constant red cell mass. As the cell matures, hemoglobin production increases, the nucleus gradually becomes pyknotic and is expelled out of the cell.
Average life
They have a half-life of approximately four months (100 to 120 days). When they lose their functional capacity they are destroyed in the spleen and liver where they are phagocytosed by macrophages and the hemoglobin is metabolized, its prosthetic group ( protoporphyrin ) contributes to form the bile pigments ( biliverdin and bilirubin ), while iron is used again. in the formation of hemoglobin.
