Haematopoiesis:Blood composed of two components.1) Blood Plasma 2) Cellular componentsThere are three types of blood cells? Red blood cells? White blood cells? platelets Production of cellular components of blood is called haematopoiesis.Haematopoiesis occurs in the bone marrow. Three types of cells are present in the bone marrow.? Stem cells? Progenitor cells? Precursor cellsStem cells;  These may be multipotential, unipotential or pluripotential, growth stimulating factors released from bone marrow and paly key role in activation of these cells to multiply. These cells can’t be differentiated by H and E stain.Progenitor cells; These may be unipotential or pluripotential with, ruminosky stain we can identify them. They have limited capacity for self-renewal and differentiation.   Precursors; They have lost their ability of self-differentiation but can divide rapidly under growth factors.When haematopoiesis starts the stem cells are divided into two types of cells.1) Myeloid stem cells2) Lymphoid stem cellsThe myeloid stem cells give rise to 6 types of blood cells.? Red blood cells? Platelets? Basophils? Eosinophils? Neutrophils? MonocytesLymphoid stem cells give rise to three types of blood cells.? B lymphocytes? T lymphocytes? Natural killer cells Erythropoiesis:Production of red blood cells in the bone marrow. Abbreviations used.CFU-GEMM                      (Colony Forming Unit- Granulocyte Erythrocyte Monocyte Megakaryocyte)IL3                                      (Interleukin 3)IL9                                     (Interleukin 9)GM-CSF                            (Granulocyte Macrophage- Colony Stimulating Factor)G-CSF                                (Granulocyte- Colony Stimulating Factor)IGF1                                 (Insulin like Growth Factor 1)EPO                                  (Erythropoietin)BFU-E                              (Erythroid – Burst Forming Unit)CFU-E                              (Erythroid Colony Forming Unit)Factors responsible for erythrocytes production include:1. Erythropoietin:   It is protein released by pre tubular interstitials cells of kidney at same time 10-15 % released from hepatocytes. Erythropoietin released when increased demand of oxygen or hypoxia. Action of erythropoietin inhibits apoptosis of progenitor cells and precursors and allows to differentiate and divide. Epo increase the synthesis of hemoglobin.2.  Interleukin 3; and interleukin 9:            It is released from sensitized t-lymphocytes, CSF, macrophages, fibroblast, endothelial cells and t-lymphocytes. They also stimulate multiplication of erythroid progenitor cells and ultimately when GM-CSF, G-CSF, BFU increases, this increase the erythrocytes3. Androgens:Their function is not very significant; they stimulate pre tubular interstitial cells of kidney to secrete more Epo so this stimulates differentiation and division of progenitor cells. Corticosteroids and estrogen inhibit the release of Epo from interstitial cells.4. Thyroid and pituitary: These increase the demand of O2 in the body which will ultimately lead to hypoxic stage, so increase O2 demand in body increase the Epo.  Pro-erythroblast, basophilic-erythroblast, polychromatic erythroblast, orthochromatic erythroblast and reticulocytes are stages of erythrocytes. In production of erythrocytes first cell size reduces then nucleus size reduces, then nucleus is excluded at orthochromtic erythroblast stage. At reticulocytes only remnant of nucleus are present. Functional cells in circulation have no nucleus. This nuclear change only occurs in blood of mammals not in avians. Mature cells pass through endothelial cells of capillaries and come in blood circulation. 

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