Hematopoiesis (blood) - the process of formation, maturation and differentiation of hematopoietic cells of the final stages of differentiation of progenitor cells in a specific microenvironment.Hematopoiesis made in the bone marrow of flat bones (skull, ribs, sternum, vertebrae, pelvis) and the epiphysis of long bones.Other hematopoietic organs are the spleen, thymus, lymph nodes and liver.In this article we consider the basic signs and symptoms of hematopoiesis in humans.
main signs of hematopoiesis
There are prenatal and postnatal hematopoiesis.
prenatal blood cells are formed in several developing bodies.
cells of the blood islands of the yolk sac to 12 weeks of fetal development form the first blood cells - primary erythroblasts - large cells containing nucleus and embryonic hemoglobin types.
During the second month of blood stem cells colonize the liver, spleen and thymus.Formed all kinds of blood cells.
Bone marrow embryo is laid by the end
mature peripheral blood cells develop from their predecessors, maturing in the bone marrow.Stem cells - CFU-blast - the ancestor of all blood cells.Stem cell characteristic morphological similarity and small lymphocytes with the ability to self-renew.They rarely and slowly multiply.Their descendants - pluripotent progenitor cells lymphocytopoiesis (CFU-Ly) and myelopoiesis (CFU-GEMM).As a result of dividing the CFU-Ly and CFU-GEMM their descendants are pluripotent or differentiated into one of several types of unipotent stem cells are also able to share, but differentiated only in one direction (forming one cell type).Unipotent of committed (differentiating) cells were morphologically different from the stem cells.They proliferate in the presence of growth factors to differentiate into progenitor cells.
- CFU-blast - Stem cells;
- CFU-GEMM - pluripotent cell myelopoiesis predecessor;
- CFU-Ly - pluripotent cell lymphocytopoiesis predecessor;
- CFU-GM - pluripotent cell predecessor granulocytes and monocytes;
- CFU-G - pluripotent cell progenitor neutrophils and basophils.
- BFU-E and CFU-E - erythrocytes;
- CFU-Eo - eosinophils;
- CFU-M - monocytes;
- CFU-Meg - megakaryocytes.
erythropoiesis from stem cells (BFU-E) differentiate unipotent precursor of CFU-E erythrocytes.Last gives rise proerythroblast.Further differentiation reduces the size and number of cell organelles therein to increase hemoglobin content and core loss.In this series of differentiated proerythroblast basophilic, polychromatic, oxyphilic erythroblast (Loevit cell), reticulocyte, erythrocyte.
During differentiation of granulocyte progenitors isolated: myeloblast, progranulocyte, medullocell, metamyelocyte, stab and segmented granulocyte.As the differentiation decreased cell size, the granules appear in the cytoplasm, the nucleus condenses and changes its shape (from rounded to the segmented).
monocytes and granulocytes have a common progenitor cell - colony-forming units of granulocytes and monocytes (CFU-GM), formed from pluripotent progenitor cells myelopoiesis (CFU-GEMM).In the development of monocytes secrete two stages - monoblast and promonotsit.
From megakaryoblasts develop very large (30-100 microns) bone marrow cells - megakaryocytes.When megakaryocyte differentiation increases in size, its core becomes lobular.Formed developed system of demarcation membranes, which separates ( "otshnurovka") platelets.
stem hematopoietic cells (CFU-blast) occurs pluripotent cell predecessor lymphopoiesis (CFU-Ly), which subsequently gives rise to cells predecessors B-lymphopoiesis, T-lymphopoiesis and (partially) predecessors of natural killer cells (NK-cells).Further differentiation includes pro-B levels (T) -cells, pre-B (T) cell populations of immature B (T) -cells, mature naive B (T) cell, and (after the contact with Ag) - mature B(T) -cells final stages of differentiation.
Education with cells activated and regulated by factors of hematopoiesis: hematopoietic growth factors, transcription factors, folic acid and vitamin B12.
Hematopoietic growth factors - stem cell factor (SCF), interleukins, erythropoietin, thrombopoietin.
transcription factors - proteins that bind to DNA and regulate gene expression of hematopoietic cells.
Folic acid and vitamin B12 are necessary for DNA synthesis.Folate and vitamin Bi2 received food and absorbed in the small intestine.For vitamin Bi2 absorption in the intestine needs biermerin synthesized by gastric parietal cells.Factor binds vitamin Bi2 and protects it from destruction by enzymes.The complex of intrinsic factor with vitamin B12 in the presence of calcium ions, interacts with epithelial cell receptors distal ileum.Thus vitamin Bi2 enters the cell and an inner factor released.Lack of intrinsic factor Castle leads to the development of anemia.
bodies of hematopoiesis and kroverazrusheniya in hematopoiesis:
By forming organs include the bone marrow (the main body of postnatal hematopoiesis), thymus, lymph nodes, spleen, Peyer's plaque intestine.The destruction of blood cells occurs mainly in the spleen.
What are the symptoms of hematopoiesis determined?
Bone marrow - the main hematopoietic organ postnatal hematopoiesis.There are bone marrow fat, active bone marrow and stroma.Yellow bone marrow (so named because of the large accumulation of fat cells) - inactive part, begins to act as needed to strengthen the hematopoietic (for example, chronic hypoxia or severe bleeding).The bone marrow is dominated maturing red blood cells that gives the bone marrow hematopoietic foci red.bone marrow stroma comprises endothelial and adventitial reticular cells (fibroblasts, bone marrow), macrophages, fat cells, osteoclasts, osteoblasts, osteocytes, and the extracellular matrix.
thymus gland (thymus) - central authority lymphopoiesis.Here comes antigennezavisimaya differentiation of T lymphocytes.Precursors of T cells fall into the cortex of the thymus from the bone marrow.The thymus consists of two lobes separated by connective tissue trabeculae.The proportion of mature thymus distinguish cortical and medullary layers.The cortical layer comprises dividing cells - precursor cells of T lymphocytes, early protimotsity having the morphology of lymphoblasts.Their subsequent differentiation into CD4 + - and CD8 + -T-lymphocytes occurs in parts of brain slices and thymus cells is the selection that can bind foreign Ar (positive selection), but can not react with its own Ar (negative selection).As a result, selection of only 3-5% of cells produced in the thymus, acquire specific markers of T-helper and T-suppressor and migrate through the medulla into secondary lymphoid organs (spleen, lymph nodes).The remaining cells are killed in the cortical layer.Moreover, thymic humoral factors produced by the immune system.
lymph node - the outside is covered with a connective tissue capsule from which trabeculae extend.In the lymph node, and brain distinguish cortical portion and sinuses.The cortical parts are located mainly in lymphocytes and macrophages, organized in primary and secondary follicles.T-lymphocytes are mainly located in the subcortical area in the center of secondary follicles.In the lymph node T cells interact with B-lymphocytes and follicular dendritic cells in the immune response.From parenchyma lymph node lymphocytes enter the efferent lymphatics.
Peyer's patches .In the course of the digestive tract in direct contact with the epithelium located lymphoid accumulations, called Peyer's patches.Their structure is similar lymphoid follicles of the spleen and lymph nodes.The main component - large germinal centers surrounded by lymphocytes.
spleen - the largest organ of the blood system, the outside covered with a connective tissue capsule.The stretching of the capsule with an increase in the spleen causing pain.The organ parenchyma distinguish red pulp (contains numerous red blood cells and macrophages which destroy old erythrocytes), white pulp (spleen lymphoid tissue collection represented accumulations of T-lymphocytes around the arteries emanating from trabecular) and lymph follicles containing accumulation of B-lymphocytes.