Erythropoiesis

Erythropoiesis (also erythropoiesis ) is the process of formation and development of erythrocytes (red blood cells). It takes place before birth in yolk sac, liver, spleen and bone marrow after birth only in the red bone marrow of the plates and short Knochen.Die erythropoiesis is stimulated by the hormone erythropoietin, which lack of oxygen in the tissues (hypoxia) is formed in the kidney. Disorders of erythropoiesis leading to anemia (anemia ).

In the 10th week of embryonic development, the proportion of liver to the body weight is 10%, at birth, only half of it - a fact which is also attributed to the function of the liver as a hematopoietic organ.

Cell differentiation

All precursors of blood cells arise from mesenchymal cells initially differentiate into all blood cells, and are therefore referred to as multipotent stem cells. Is a development path once taken, the cell loses its ability to enter into other paths of development, they are now referred to as unipotent stem cell.

The unipotent stem cell of the erythrocyte is called the " Erythropoietin -responsive cell" (ERC). It develops over Proerythroblast, erythroblast, reticulocyte normoblast and to erythrocytes ( normocyte ). The development cycle in the bone marrow (up to the reticulocyte ) takes about five to nine days. Every day for the replacement of outdated erythrocytes in humans approximately 200 billion (0.8% of the total) formed red blood cells again.

Proerythroblast

Proerythroblasts (also: Präerythroblast from Greek blastos "seed" ) are roundish, 16-18 microns large cells with large, pale nucleus containing two nucleoli and increasingly basophilic ( dyeable with basic dyes ) cytoplasm. A Proerythroblast through the cell divisions in the further differentiation in the formation of red blood cells 16. After the division of proerythroblasts, basophilic erythroblasts arise first.

Erythroblast

The first stage of development are the basophilic erythroblasts. Their nuclei are relatively small and contain clumped chromatin. With further reduction of the core size and decrease in basophilia the polychromatic erythroblasts now occur ( macroblasts ). This synthesize the polyribosomes the red blood pigment hemoglobin and accumulate it in the cell, whereby the cytoplasm is increasingly used for acid dyes dyeable ( acidophilic ) and finally the normoblast arises.

Normoblast

As normoblasts two cell types are summarized, where a relatively condenser, round nucleus and homogeneous gray pink cytoplasm are acting in common. The still capable of dividing immature cell with cytoplasm graublaustichigem is now known as polychromatic and the distribution incompetent, more hemoglobin- containing form with is starting to pink color of the cytoplasm as orthochromatic erythroblast. In this last form of nuclear condensed to a small, black and structureless beads which is finally ejected. The now seedless young erythrocyte is rich in ribosomes, which can be obtained by special stains to network- like structures ( substantia reticulo - filamentosa ) failures, the reticulocyte.

Reticulocyte

Reticulocytes are juvenile red blood cells and occur 1-2 days after the gutting of the normoblasts in the bone marrow. In contrast to erythrocytes they still contain RNA and cell organelle remnants and are even larger than this. This RNA residues are also called substantia granulofilamentosa. Their name from the reticulocytes of the staining of the ribonucleoprotein of the ribosomes, which in the supravital staining or staining with brilliant cresyl blue as a fine reticular drawing in the cytoplasm ( reticulum, the diminutive of rete " net" is ) presents itself.

Reticulocytes migrate from the bone marrow into the blood, and mature here to the erythrocytes. Normal trained in size, shape and staining behavior erythrocytes are also referred to as normocytes.

A change in the number of reticulocytes in the peripheral blood (normal 3-18 ‰) may provide clues to an enhanced or lack of erythropoiesis, which is to distinguish the forms of anemia of practical importance.

Regulation

The formation is regulated by an enzyme ( renal Erythropoesefaktor, REF ), which is discharged at a reduced oxygen saturation in the blood by the kidney. This enzyme cleaves a protein of the blood plasma from the hormone effective erythropoietin ( "EPO " ), which stimulates the division of the ERC.

An increased need for red blood cell formation in the bone marrow to the eight to ten times the normal production can be increased. An increased need may arise through increased death of red blood cells ( hemolytic anemia, hemolysis), by hemorrhage or, for example staying in greater heights with the connected thereby lower oxygen partial pressure. Also, administration of erythropoietin leads to an increase in hematocrit and applies to sports as doping. The number of reticulocytes also can be increased by the administration of G -CSF on their natural limit.