The erythrocyte deformability or flexibility of red blood cells enables the cells to pass through vessels with different lumens. In addition, erythrocytes change shape depending on the temperature and flow rate of the blood, with concomitant changes in blood viscosity. Abnormal shape is assumed by erythrocytes in the context of spherical or sickle cell anemia, for example.
What is erythrocyte deformability?
Red blood cell deformability, or flexibility, enables the cells to pass through vessels with different lumens. Red blood cells are also called erythrocytes. The blood cells contain the so-called hemoglobin and are thus responsible for the transport of oxygen in the human body. Oxygen is needed by all body tissues for survival. In the area of the lungs, oxygen passes into the blood, where it is present in unbound and bound forms. Binding affinity exists between oxygen and the hemoglobin of red blood cells in the environment of the lungs. Bound to the red blood cells, oxygen travels with the blood to all parts of the human body. Because the milieu changes bit by bit on its journey through the body, reducing the binding affinity, the oxygen is eventually released again and absorbed by the target tissues. Red cell deformability is one of the most important properties of red blood cells. Because of their flexibility, erythrocytes are able to,
pass with the blood through the narrowest vessels and pass through the smallest-lumen capillaries. This phenomenon is particularly relevant for the oxygen supply of all body tissues. Thus, the deformability of the erythrocyte membrane enables the red blood cells to pass through the thinnest pores. With each change in the shape of the erythrocytes, the flow properties and viscosity of the blood change.
Function and purpose
The shape of red blood cells increases their surface area, allowing for improved gas exchange. Because of their high flexibility, erythrocytes can also migrate through capillaries that are smaller in diameter than the erythrocytes themselves. Particularly when passing through narrow capillaries, erythrocytes deform or, as part of pseudoagglutination, aggregate into rouleaux. Beneath the cell membrane of red blood cells lies an irradiating network of structuring and densely arranged filaments called the erythocytic cytoskeleton, which serves to maintain a biconcave shape. Proteins such as spectrin and ankyrin are essential components of cells and contribute to their deformability. Apart from their typically biconcave shape, erythrocytes can assume divergent shapes thanks to their flexibility. In their basic shape, red blood cells are called discozytes. The blood cells assume this biconcave disk shape in flowing blood. However, several dozen different shape variants exist. In narrower capillaries, for example, the cells become stomatocytes and in this context are in a folded cup shape, which facilitates their passage through the narrow-lumen capillaries. In contrast, dacryocytes are teardrop-shaped and echinocytes are datura-shaped erythrocytes, as found in hypertonic solutions. The flexibility of erythrocytes proportionally influences blood viscosity in particular. This refers to the viscosity of the blood, which combines the material properties with the properties of liquids. Due to its viscosity, blood shows an adapted flow behavior and does not behave like a Newtonian fluid. Its flow behavior is not proportional, but erratic. Responsible for this, besides the Fåhraeus-Lindqvist effect, are the hematocrit, the temperature and the flow velocity. The erythrocyte deformability including erythrocyte aggregation plays a major role in this connection. These interrelationships allow the blood to flow differently in different parts of the body and prevent the cellular blood components from clumping together. At low flow rates in the blood, erythrocytes attach to each other sporadically and form chains. This money roll formation or agglomeration can be understood as physiological to some extent.
Diseases and disorders
In the context of various diseases, the deformability of erythrocytes is impaired.In yet other diseases of the blood system, red blood cells are present in abnormal shape variants. Any abnormality of the red blood cell shape or reduction of their deformability affects the blood viscosity and can have correspondingly severe consequences. For example, in the form of the so-called acanthocyte, red blood cells are present as spiny cells. Erythrocytes assume this shape, for example, in the case of disorders of phospholipid metabolism. Anulocytes, on the other hand, are ring-shaped erythrocytes, as present in high-grade anemias. In the form of fragmentocytes, erythrocytes occur in the phenomenon of intravascular hemolysis. Macrocytes are also a pathological form variant of red blood cells. In this case, the erythrocytes are greatly enlarged, as may be the case, for example, in folic acid deficiency. In megaloblastic anemia, the red blood cells are also enlarged. This form variant is called megalocyte. The blood components are reduced in size to so-called microcytes in iron deficiency diseases and hemoglobin deficiency diseases. One of the best known form diseases of erythrocytes is spherical cell anemia, in which the red blood cells appear as spherically small microspherocytes. Similarly known as spherical cell anemia, is sickle cell anemia. In this disease, the red blood cells change their physiological shape to a sickle shape, called sickle cell. In the context of iron deficiency, perniciosa, and bone marrow lesions, the cells in turn assume the abnormal shape of poikilocytes. In contrast, the red blood cells are present as target cells in the context of thalassemias, toxic anemias or iron deficiency anemias. This form variant is characterized by the ring-shaped arrangement of hemoglobin. Also after mechanical damage, erythrocytes change their shape to an abnormal form: the so-called schistocyte. These are deformed erythrocytes that ultimately resemble only a fragment of red blood cells. Increased gel roll formation of erythrocytes refers to inflammatory phenomena in the context of immune complex diseases.
