Erythrocytes comprise quantitatively the largest portion of the peripheral blood cell mass. Their normal range is between - x 1012/L. Erythrocytes are easily recognized. They stain eosinophilic, i.e. they are orange-red, round, have a central pallor and have no nucleus. Erythrocytes normally exhibit high uniformity which is why they are suitable as a standard for other cells. Less than 10% normally show an abnormality in size, shape, or color.
Erythrocytes measure about 7 µm in diameter. In order to identify size abnormalities, the nucleus of a small lymphocyte can be used as a norm. The shortest diameter of the red cell is approximately 7-8 µm.
The erythrocyte form resembles a disc, that is indented in the middle on both sides, or biconcave. This creates the central pallor.
The erythrocyte's color indicates that they are filled with hemoglobin. The central pallor usually constitutes 1/3 of its diameter. If the diameter measures more than one third, then hypochromia is present, i.e. the erythrocytes appear brighter and/or less well-stained. Hyperchromia can also occur. In this case, the erythrocytes appear darker and the central pallor is either absent (spherocyte) or very small. This is only observed in hereditary spherocytosis.
Erythrocytes have a uniform cytoplasmic staining. Erythrocytic inclusions are always pathological when present in the peripheral blood.
Erythrocytes are extraordinary cells in many respects. They transport oxygen and other molecules. The transportation of immune complexes on the cell surface to the spleen and liver, for example, is important. The erythrocyte shape has two decisive advantages. First, an ideal volume-surface ratio results that is important for the exchange of gases. Second, this shape provides for deformability, which is of decisive importance for passage through capillaries. Not having a nucleus also provides a number of advantages. This helps make deformability easier. The heart also benefits, which the following theoretical calculation illustrates. The heart pumps approximately 3 kg of erythrocytes per minute through a person weighing 75 kg. Since a cell nucleus weighing 40 pg is 50% of the weight of an erythrocyte of 100 pg, this creates a savings of one to one and a half fewer tons per day that the heart has to pump.