Erythrocytes, or red blood cells are cells that humans and mammals deprived kernel and have a homogeneous protoplasm.
In the structure of erythrocyte distinguish stroma - a skeleton of a cell and the surface layer of the shell. The membrane of the red blood cells are formed lipidnog-protein complexes; it impervious to colloids and ions K and Na and permeable for anions Cl', NSOs'3 and ions N and IT'. The mineral composition of erythrocytes and plasma varies: in human erythrocytes more potassium than sodium, plasma there is an inverse relationship of these salts. 90% dry matter of erythrocytes is the hemoglobin, and the remaining 10% - other proteins, lipids, glucose, and mineral salt.
For physiology and clinics significant has been the determination of the number of red blood cells, which produce under the microscope using the accounts chambers or automatically using existing electronic devices.
1 mm3 the blood of men contains about 5 000 000 erythrocytes, women - about 4 500 000. In newborns, the number of erythrocytes more than adults.
The number of red blood cells may change. It increases with low barometric pressure (while climbing to the heights), muscular effort, emotional excitation, if the loss of the body of water. The increase in blood red blood cell counts may take different time and not necessarily mean increased their total number in the body. So, with a huge loss of water caused by, for example, profuse sweating, is short-clotting of the blood and therefore the number of red blood cells in a unit volume increases, although the absolute number in the body and does not change. In an emotional arousal and severe muscle number of red blood cells increases due to the reduction in spleen and revenues in total blood stream of blood, rich in red blood cells, of splenic blood depots.
The increase in the number of red blood cells in the conditions of stay at reduced barometric pressure due to low oxygen in the blood. People living in mountainous areas, the number of red blood cells increases due to their intense production by the bone marrow - body blood (Fig. 3). In this case, not only increases the number of red blood cells per volume of blood, but their total number in the body.
The decrease in the number of erythrocytes in blood, anaemia is observed after blood loss or due to increased destruction of red blood cells or weakening of their education.
The diameter of a single human erythrocyte equal to 7,2-7,5 MK, and the volume of go about 88-90 mk3. The size of individual erythrocytes and total number of them in the blood determine the amount of their total surface. This value is of great importance because it determines the total surface on which occur absorption and delivery of oxygen, i.e.
the process, which is the main physiological function of erythrocytes.
The total surface of all human blood cell is approximately 3000 mg, i.e. 1500 times more surface of the whole body. Such a large surface contributes to the peculiar shape of the erythrocyte. The human erythrocytes have tapered shape with the impressions inside in the middle on both sides (Fig. 4). In this form in erythrocyte there is no point at which defended more than 0,85 MK from its surface, while at the spherical form the centre of the cell would be from it on distance of 2,5 MK, and the total surface would be 20% less. Such relationships of surface and volume contribute to better implementation of the basic function of erythrocyte - to transfer oxygen from the respiratory organs to the body cells.
This function is carried out due to the availability of erythrocyte respiratory pigment blood hemoglobin.
The fact that hemoglobin is found inside red blood cells and not dissolved in the blood plasma is important physiological value. As a result of this:
1. Decreases viscosity of the blood. Calculations show that the dissolution of the same quantity of hemoglobin in the blood plasma would increase several times the viscosity of the blood, and severely hampers the work of the heart and circulation.
2. Reduced plasma oncotic pressure of the blood that are important to prevent dehydration of tissues (due to the transition of tissue water in the blood plasma).
3. Creating optimal conditions for the binding of oxygen hemoglobin due to the presence of a special chemical environment inside the erythrocyte.

Fig. 3. The change in the number of hemoglobin and erythrocytes participants Alpine expedition depending on height above sea level (at the Pace and others).
Fig. 4. Schematic representation of an erythrocyte.