How does thrombocytopoiesis take place? The thrombocytopenic megakaryocyte will emit cytoplasmic expansions which will pass through the pores of the sinusoid capillaries and these expansions which are initially packages of azurophilic granulations surrounded by demarcation membranes which are held together by cytoplasmic bridges. In the circulatory torrent there will be a weakening and therefore a segmentation into platelets. It can happen that the thrombocytopenic megakaryocytes pass into the circulatory torrent and these large elements will get blocked in the pulmonary capillaries where they will explode and at that moment they will also release the platelets. The monocytic lineage 2 main stages identified. - 1 stadium is the monoblast. It closely resembles the myeloblast with fine, slightly more combed chromatin. 2 to 5 nucleoli. A cytoplasm is basophilic. This is an element larger in size than the myeloblast: 25 to 30 micrometers. Then the element a little more mature is: - the promonocyte :We are more helped morphologically because the nucleus takes on a kidney-shaped appearance. This promonocyte becomes a: - Monocyte :which is no longer nucleolated while the previous one is still nucleotide. In this lineage we find peroxidases and esterases which are non-specific but which are inhibited by sodium fluoride. The lymphoid lineage Precursors: lymphoblasts are small elements with very fine chromatin, a central nucleus, and a high N/P ratio. Lymphoblasts resemble cell hematopoietic strains from a morphological point of view. B and T lymphoid cells have a common progenitor which differentiates very early from the stem cell. After this progenitor goes either towards the B lineage and at this time maturation takes place in the MOH, at the same time as there is maturation of this B lymphoid element there is rearrangement of the immunoglobulin genes. The mature but naive element that has not yet been in contact with an antigen will carry type M or D immunoglobulins. The precursor for T lymphocytes leaves the MOH to go into the thymus where the education of T lymphocytes will take place as well as the maturation. In MOH, we highlight a few lymphocytes which have recirculated, this is the Homing phenomenon:They will leave the MOH and then they will come back. How to explore the MOH? - Qualitative exploration :is done by the myelogram so we use a trocar of Mallarmé that we planted at the level of the sternal manubrium so we cross the bony cortex and then we will aspirate the MOH. We recover blood but marrow grains and these are the latter which we will crush between blade and lamella and at the level of these grains we put in place highlights the elements of the different lineages. The myelogram can also be performed at the posterior iliac crest. If the patients have been irradiated in the thorax, a myelogram is done on a non- irradiated area. - Proportion of different lineages:The important thing is to see that the granular lineage is very well represented and in the majority compared to other lineages.
- Quantitative analysis: 1) We do an osteo medullary biopsy. It only happens at the iliac crest.posterior ue. We use a troccart which is 20 cm long, 3 mm in external diameter and 2 in internal diameter and generally we remove a bone core 2 cm long and 2 mm wide. diameter. It's a difficult act. 2) We can make iron 59 scintigraphy and this makes it possible to evaluate erythropoiesis therefore the formation of red blood cells. When we do myelograms we can also do cell cultures, we collect the cellular elements on a heparinized tube and then we culture the elements and we will see what types of progenitors we mainly have, what lineages do they give?