Hematopoietic Cells

Hematopoietic cells 1) The erythroblast lineage :is the origin of red blood cells. Features :As maturation occurs, hemoglobin is synthesized and densifies the core. Morphology :When we do a myelogram we can see the different stages of maturation therefore the different cell types during evolution which are arranged around a macrophage, a reticular cell, this is what we call the island erythroblastic. ➔ 1 identifiable morphological element, that is, it is the proerythroblast:It has an average size, 20 to 25 micrometers in diameter. The chromatin is thin. There are 2 nucleoli. The cytoplasm is very basophilic (ultramarine blue). The cytoplasm does not contain granulations. ➔ The proerythroblast gives rise to 2 basophilic erythroblasts which is an element of smaller size, a round nucleus in a central position, the cytoplasm still very basophilic but the chromatin is a little more condensed and we no longer find a nucleolus. ➔ This basophilic erythroblast gives rise to 2 polychromatophilic erythroblasts . The size decreases further (9 to 12 micrometers in diameter). Chromatin becomes denser: it is cold. The cytoplasm is loaded with hemoglobin and it will take on a pinkish gray color. This is why this element is called “polychromatophilic”. ➔ This element divides and gives 2 acidophilic erythroblast which are said “ normoblasts' ' : the chromatin is very dense. The core is often in an eccentric position. The cytoplasm is acidophilic due to the presence of a high concentration of hemoglobin. At this stage there are: ➔ Expulsion of the nucleus and in the remaining cytoplasm there are some mitochondria, rRNA highlighted by the vital stains so here it is the reticulocyte which remains for 24 hours in the MOH then passes into the blood for 24 hours and will then become a erythrocyte . ➔ This diagram shows that from a proerythroblast we have 2 basophilic erythroblasts, one subdivision into polychromatophilic erythroblast and from the last acidophilic stage we have no more division and there we see that each time there is an increase in the concentration of hemoglobin. The whole phenomenon lasts a week. The erythrocyte will remain 120 days in the circulatory torrent and when it becomes senescent it will be destroyed largely by the macrophages which are also present in the MOH. 2) The granular lineage For the neutrophil, eosinophil and basophil lineage, differentiation in one of the pathways (neutro, basoor eosino) is done well upstream of the myeloblast stage, that is to say when we start from a myeloblast this element is already oriented and programmed to become either a base or an eosino or a neutro but from a point of morphological view we cannot say how it is programmed. The final stage of this myeloblast is a polynuclear cell. - The myeloblast: is an element that is between 15 and 25 micrometers in diameter. The chromatin is fine, it is oriented slightly combed. 2 to 5 nucleoli are highlighted at the level of the nucleus. The cytoplasm is basophilic and we can highlight from a few azurophilic granulations to very numerous azurophilic granulations. This myeloblast will divide and give: - the promyelocyte :the chromatin densifies a little but remains quite fine. We can put still visible nucleoli. The difference compared to the myeloblast is essentially in the cytoplasm, in front of the nucleus the presence of a clear zone that we called “sarcoplasm”, this zone corresponds to laying eggs at the location of the golgi apparatus. In the cytoplasm reveals numerous azurophilic granulations and this promyelocyte gives rise to:

- 2 myelocytes :At the myelocytic stage, specific lineage granulations (important) will appear, either beige (neutro) or large orange granulations of eosino or metachromatic granulations which appear black on MGG for basophilia. At this stage the chromatin is more condensed without appearing in clumps as for polynuclear cells. We no longer highlight the nucleoli and there is persistence of azurophilic granulations in the cytoplasm. As the evolution progresses, the azurophilic granulations will be less present. - The metamyelocyte: At this stage we have a nucleus that elongates, curves especially for neutrophils, a little less for eosinophils. From this stage there is no more division, we simply have a maturation so the neutrophilic metamyelocyte will give 1 polynuclear neutrophil etc. PFor the neutrophil line, the stretching of the nucleus will be very important since afterwards we have a segmentation and a polylobed appearance (at least 3 lobes) whereas for the eosino it is never more than 2 lobes. The eosinophil lineage is essentially sensitive to - L'interleukin 5 and the basophil to interleukin 3 and the mast cell is the stem cell factor.