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Questions and Answers
The most immature recognizable cell in the myeloid series is the myeloblast, which has a finely dispersed chromatin and faint nucleoli.
True
Promyelocytes are characterized by their eosinophilic cytoplasm and specific granules containing lysosomal enzymes.
False
During the metamyelocyte stage, the nuclei of neutrophilic, basophilic, and eosinophilic metamyelocytes exhibit a distinct polymorphic appearance.
False
A reticulocyte is formed after the orthochromatic erythroblast undergoes enucleation and primarily consists of ribosomes and hemoglobin.
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After maturation, reticulocytes transform into erythrocytes within a time frame of 3-4 days.
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The total time required for a myeloblast to produce mature, circulating neutrophils ranges from 14 to 18 days.
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Megakaryoblasts undergo endomitosis, resulting in a highly polyploid nucleus that ranges from 8N to 64N.
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Neutrophils can adhere loosely to endothelial surfaces in venules and small veins, a process known as margination.
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Proplatelets are short and narrow extensions that do not penetrate adjacent microvascular endothelium.
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Platelets originate from the fragmentation of mature erythrocytes in the bone marrow.
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Study Notes
Myeloblasts and Granulocyte Development
- Myeloblasts represent the most immature identifiable cell in the myeloid lineage, characterized by finely dispersed chromatin and faint nucleoli.
- Promyelocytes exhibit basophilic cytoplasm and contain azurophilic granules with lysosomal enzymes and myeloperoxidase; different gene activation leads to the development of distinct granulocyte lineages.
- Myelocyte stage marks the initial visible differentiation, where specific granules begin to increase in quantity.
- In the metamyelocyte stage, granules dominate the cytoplasm, and nuclei condense in neutrophilic, basophilic, and eosinophilic forms during maturation.
- Band cells represent an intermediate stage before full maturation of neutrophilic granulocytes, featuring elongated but not polymorphic nuclei.
Erythrocyte Development
- Hematopoietic stem cells (HSCs) in bone marrow are pluripotent and capable of differentiating into various blood cells.
- HSCs progress into myeloid progenitor cells, specifically committed to the erythroid lineage.
- Proerythroblasts emerge as the first recognizable erythroid stage, capable of mitosis.
- Basophilic erythroblasts develop from proerythroblasts with abundant ribosomal RNA, which imparts a blue color upon staining.
- Polychromatophilic erythroblasts arise as hemoglobin synthesis initiates, showing mixed blue and pink staining due to both ribosomes and hemoglobin presence.
- Orthochromatic erythroblasts, or normoblasts, evolve from polychromatophilic erythroblasts, featuring a predominantly pink cytoplasm from increased hemoglobin and a condensing nucleus.
- Reticulocytes form after orthochromatic erythroblasts expel their nuclei; they still retain some organelles and ribosomes, primarily comprising hemoglobin.
- Mature erythrocytes develop from reticulocytes in circulation within 1-2 days, fully losing organelles and completing maturation.
- Total duration from myeloblast to circulating mature neutrophils is 10 to 14 days, involving five mitotic divisions during earlier stages.
Neutrophil and Platelet Dynamics
- Neutrophils exist in four compartments: granulopoietic compartment, storage in marrow, circulating population, and marginal pool along venular endothelium; margination may last hours without subsequent emigration.
- Platelets, or thrombocytes, originate by fragmentation from mature megakaryocytes, which differentiate from megakaryoblasts under thrombopoietin influence.
- Megakaryoblasts are characterized by a diameter of 25-50 μm with basophilic cytoplasm and a large, multi-nucleolated nucleus; they undergo endomitosis resulting in a highly polyploid nucleus.
- Mature megakaryocytes can reach up to 150 μm in diameter with large, irregularly lobulated nuclei consisting of coarse chromatin and abundant organelles.
- Platelet formation involves megakaryocytes extending proplatelets into the microvasculature, where actin and microtubules facilitate transport of membrane vesicles and granules.
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Description
This quiz covers the stages of myeloblast and erythrocyte development. It highlights the characteristics and changes during the maturation of granulocytes and red blood cells from hematopoietic stem cells. Test your understanding of these critical processes in hematopoiesis.
