Function and regulation of the hematopoietic bone marrow OMOH has an important production role because this system must produce 10 1 ê 3 blood cells per day to compensate for losses and this continues. Cells hematopoietic cells are divided into 3 compartments of unequal importance: pluripotent stem cells Progenitors already involved in certain lineages/The precursors. OThe pluripotent cell is dormant but can also enter a cycle. It can differentiate to give either a lymphoid progenitor or a mixed progenitor. These are elements which are not morphologically identifiable: they are not precursors but progenitors. For progenitors we use CFU for colony forming units: these are cells capable of forming colonies in cell culture. This element gives clumps of cells in culture which can then differentiate according to the cytokines that can be add to the medium either towards the erythroblastic or megakaryocytic, granular lineage or monocytic, this is why we say CFU: G for granular, E for erythrocyte, N for megakaryocytic and M for monocytic So CFU G, E, N. M: a mixed progenitor. From this mixed progenitor we can have the erythroblastic lineage, BFU for burst forming units which is another type of colony. From this mixed progenitor we have the possibility of having a megakaryocytic progenitor or a progenitor that is still mixed which makes both granulocytes and monocytes. The progenitors for eosinophils and basophils are different from that which will give rise to the progenitor for either the granular (the neutrophil) or the monocytes. The eosinophil lineage is very sensitive to Interleukin 5 and basophil to interleukin 1. OMOH has a role in the release of cellular elements that we dislike in Diabase. This release generally only concerns mature elements It's a trans passage endothelial cell and generally the pore diameter of sinusoidal capillaries is less than the size of the elements and there are only mature cells which have the capacity to deform and therefore to be able to pass through these pores. The orifices are not permanent and the elements which want to pass must have the possibility of migrating and deforming Diabase is regulated by erythropoietin which will promote the passage of reticulocytes into the blood OWe can also have bacterial endotoxins which can modify the diameter of the pores: for example in cases of pneumococcal pneumonia which are severe bacterial infections, we can have immature elements of the granular lineage therefore for example metamyelocytes or neutrophil myelocytes in the circulating blood because the MOH is stimulated in its production and at this time we have released polynuclear neutrophils, we have a large production and some immature elements can pass. There can be passage of other immature elements in pathological circumstances: for example if the medullary cavities are occupied by things other than MOH, it could be an invasion by malignant cells/cancer and at this moment these cells take the place of the MOH and push out the immature elements. OMOH has a role in uptake and phagocytosis since there are numerous macrophages in the MOH. It may be an uptake of bacteria and phagocytosis of senescent erythrocytes and macrophages send cytoplasmic extensions through the endothelial cells.
-Regulation of hematopoiesis: The important thing is the economy of cell strains. We have our totipotent stem cell which is dormant and this cell has the capacity to self-renew without necessarily triggering a phenomenon of cellular differentiation and At this point the stem cells can once again be dormant Either the stem cell will engage in a path of differentiation, the fact that it remains dormant for example, TGF beta will promote maintenance in a dormant or quiescent state by a weak response to growth factors and also due tone increase in the P27 protein which inhibits cyclin dependent kinase and therefore stops the cell cycle. If the concentration of TGF beta 1 decreases or we give anti-TGF, at that moment we have a drop in P27, an entry into the cycle and the expressionession of receptors for example for the stem cell factor, receptors for interleukin 8, for other growth factors, a decrease in CD34. This does that the cell becomes activated Not only is there a modification of the receptors for growth factors but there are also modifications for molecules which allow adhesions between cells: for example we have transmembrane receptors called NOTCH and JAG. These molecules are members of a superfamily of receptors including evolution JAG molecules can be carried by stromal cells therefore fibroblasts and NOTCH molecules by hematopoietic cells and if we have high expression levels of these receptors we now have dent of the stem cells in an undifferentiated state otherwise we have modifications of the transcription factors and at this time the cells start to cycle.
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Function and Regulation of the Hematopoietic Bone Marrow