Erythrocyte: structure, form and function. Structure of human erythrocytes

The erythrocyte is a blood element that is able to transport oxygen to tissues due to hemoglobin, and carbon dioxide to the lungs. This is a simple cell with a structure that is of great importance for the life of mammals and other animals. Erythrocyte is the most numerous type of body cells : about a quarter of all cells in the body are red blood cells.

General patterns of erythrocyte

Erythrocyte - a cell that originated from the red germ of hematopoiesis. On the day of such cells, about 2.4 million are produced, they enter the bloodstream and begin to perform their functions. During the experiments it was determined that in the adult human erythrocytes, whose structure is significantly simplified in comparison with other cells of the body, live 100-120 days.

In all vertebrates (with rare exception) from the respiratory organs to the tissues, oxygen is transferred by means of hemoglobin of erythrocytes. There are exceptions: all representatives of the family of "protein" fish exist without hemoglobin, although they can synthesize it. Since at their temperature, oxygen dissolves well in water and blood plasma, its more massive carriers, which are red blood cells, are not required for these fish.

Erythrocytes of chordates

In a cell like the erythrocyte, the structure is different depending on the class of chordates. For example, in fish, birds and amphibians, the morphology of these cells is similar. They differ only in size. The form of erythrocytes, the volume, size and absence of some organelles distinguish mammalian cells from others, which are found in other chordates. There is also a regularity: the erythrocytes of mammals do not contain superfluous organelles and the cell nucleus. They are much smaller, although they have a large contact surface.

Considering the structure of erythrocytes of a frog and a human, common features can be identified immediately. Both cells contain hemoglobin and are involved in oxygen transport. But human cells are smaller, they are oval and have two concave surfaces. Erythrocytes of frogs (as well as birds, fish and amphibians, except salamander) are spherical, they have a nucleus and cellular organelles, which can be activated if necessary.

In human erythrocytes, as well as in the red blood cells of higher mammals, there are no nuclei and organelles. The size of the goat's erythrocytes is 3-4 microns, the human 6.2-8.2 microns. In amphium (caudate amphibian), the cell size is 70 μm. Obviously, the size here is an important factor. The human erythrocyte, although smaller, has a larger surface due to two concavities.

The small size of the cells and their large number allowed to multiply the ability of the blood to bind oxygen, which now depends little on external conditions. And such features of the structure of human erythrocytes are very important, because they make it possible to feel comfortable in a certain habitat. This is a measure of adaptation to life on land, which began to develop even in amphibians and fish (unfortunately, not all fish in the process of evolution were able to colonize land), and reached a peak in the development of higher mammals.

Structure of human erythrocytes

The structure of blood cells depends on the functions that are assigned to them. It is described from three angles:

1. Features of external structure.
2. Component composition of erythrocyte.
3. Internal morphology.

Externally, in profile, the erythrocyte looks like a biconcave disk, and in full face - like a round cage. The diameter is normally 6.2 to 8.2 microns.

More often in the blood serum there are cells with small differences in size. With a lack of iron, the run-up decreases, and anisocytosis is recognized in the blood smear (many cells with different sizes and diameters). With a deficiency of folic acid or vitamin B _{12, the} erythrocyte increases to megaloblast. Its size is about 10-12 microns. The volume of a normal cell (normocyte) is 76-110 cu. M.

The structure of erythrocytes in the blood is not the only feature of these cells. Much more important is their number. Small sizes allowed to increase their number and, consequently, the area of the contact surface. Oxygen is more actively captured by human erythrocytes, rather than frogs. And most easily it is in tissues from human erythrocytes.

The amount is really important. In particular, an adult in a cubic millimeter contains 4.5-5.5 million cells. The goat has about 13 million erythrocytes in a milliliter, while the reptiles have only 0.5-1.6 million, fish have 0.09-0.13 million in a milliliter. In a newborn child, the number of red blood cells is about 6 million in a milliliter, and for the elderly, less than 4 million per milliliter.

Functions of red blood cells

Red blood cells - red blood cells, the number, structure, functions and development features of which are described in this publication, are very important for humans. They implement some very important functions:

• Transport oxygen to tissues;
• Carry carbon dioxide from tissues to the lungs;
• Bind toxic substances (glycated hemoglobin);
• Participate in immune reactions (immune to viruses and due to active forms of oxygen are capable of damaging effects on blood infections);
• Are able to tolerate certain medicinal substances;
• Participate in the implementation of hemostasis.

We continue our consideration of such a cell as the erythrocyte, its structure is maximally optimized for the implementation of the above functions. It is as light and mobile as possible, has a large contact surface for gas diffusion and chemical reactions with hemoglobin, and also rapidly divides and replenishes losses in the peripheral blood. This is a highly specialized cell, whose functions can not be replaced.

Erythrocyte membrane

In a cell like the erythrocyte, the structure is very simple, which does not apply to its membrane. It is 3-ply. The mass fraction of the membrane is 10% of the cell membrane. It contains 90% of proteins and only 10% of lipids. This makes the erythrocytes special cells of the body, since in almost all other membranes, lipids predominate over proteins.

The volume form of erythrocytes due to the fluidity of the cytoplasmic membrane can vary. Outside the membrane itself is a layer of surface proteins that have a large amount of carbohydrate residues. These are glycopeptides, under which is located a bilayer of lipids, facing the hydrophobic ends inside and out of the erythrocyte. Under the membrane, on the inner surface is again a layer of proteins that do not have carbohydrate residues.

Receptor complexes of erythrocyte

The function of the membrane is to ensure the erythrocyte is deformable, which is necessary for capillary transmission. In this case, the structure of human erythrocytes provides additional opportunities - cellular interaction and electrolyte current. Proteins with carbohydrate residues are molecules of receptors, due to which the erythrocytes are not "hunting" for CD8-leukocytes and macrophages of the immune system.

Erythrocytes exist due to receptors and are not destroyed by their own immunity. And when, due to repeated pushing through capillaries or due to mechanical damage, red blood cells lose some receptors, the spleen macrophages "extract" them from the blood stream and destroy them.

Internal structure of erythrocyte

What is the red blood cell? Its structure is of no less interest than functions. This cell is similar to a bag with hemoglobin bounded by a membrane on which the receptors are expressed: differentiation clusters and various blood groups (according to Landsteiner, Rhesus, Duffy and others). But inside the cell is special and very different from other cells of the body.

Differences are as follows: red blood cells in women and men do not contain a nucleus, they do not have ribosomes and endoplasmic reticulum. All these organelles were removed after the cell was filled with hemoglobin. Then the organelles were unnecessary, because to push through the capillaries required a cage with minimal dimensions. Therefore, inside it contains only hemoglobin and some auxiliary proteins. Their role is not yet clear. But because of the lack of endoplasmic reticulum, ribosomes and nucleus, it has become light and compact, and most importantly, it can easily deform together with the fluid membrane. And these are the most important features of the structure of red blood cells.

Erythrocyte life cycle

The main features of red blood cells are their short life. They can not divide and synthesize the protein due to the nucleus removed from the cell, and therefore structural damage to their cells accumulates. As a result, the erythrocyte is characterized by aging. However, hemoglobin, which is captured by the spleen macrophages during the death of red blood cells, will always be sent to the formation of new oxygen carriers.

The life cycle of the erythrocyte begins in the bone marrow. This organ is present in lamellar matter: in the sternum, in the wings of the iliac bones, in the bones of the base of the skull, and also in the cavity of the femur. Here, the precursor of myelopoiesis with the code (CFU-GEMM) is formed from the stem cell of the blood under the action of cytokines. After division, it will give the ancestor of hemopoiesis, denoted by the code (BOE-E). It forms the precursor of erythropoiesis, which is indicated by the code (CFU-E).

This same cell is called the colony-forming cell of the red blood sprout. It is sensitive to erythropoietin - a substance of hormonal nature secreted by the kidneys. Increasing the amount of erythropoietin (on the principle of positive feedback in functional systems) accelerates the processes of division and production of erythrocytes.

Erythrocyte formation

The sequence of cellular bone-marrow transformations of CFU-E is as follows: an erythroblast is formed from it, and from it a pro-monocyte giving rise to a basophilic normoblast. As protein accumulates, it becomes a polychromatophilic normoblast, and then a oxyphilic normoblast. After removing the nucleus, it becomes a reticulocyte. The latter enters the bloodstream and differentiates (ripens) to a normal red blood cell.

Destruction of erythrocytes

Approximately 100-125 days the cell circulates in the blood, constantly transfers oxygen and removes metabolic products from the tissues. It transports the carbon dioxide associated with hemoglobin and sends it back to the lungs, simultaneously filling its oxygen molecules with oxygen. And as the damage is received, it loses the molecules of phosphatidylserine and the receptor molecules. Because of this, the erythrocyte falls under the "sight" of the macrophage and is destroyed by it. And heme, obtained from all digested hemoglobin, is again sent for the synthesis of new red blood cells.