To start with, let us break down the word itself, “erythro” in Greek means “red” and “poiesis” means “to make.”
So, it is the process that produces RBC (erythrocytes) from pluripotent hematopoietic stem cells. There are various stages in erythropoiesis.
Let us dive deep and study each stage and the changes occurring in the stem cells that give rise to the RBCs.
The Mechanism of Erythropoiesis
The pluripotent hematopoietic stem cell, in the presence of transcription factors like GATA & friend of GATA (FOG), forms the burst forming unit - Erythrocyte (BFU-E).
BFU-E consists of the earliest committed erythroid progenitor cells.
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The BFU-E gives rise to the colony-forming unit (CFU-E). The unique property of CFU-E is that it has numerous erythropoietin (EPO) receptors.
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A large chunk of the erythropoietin in the body is produced in the kidneys and they act on CFU-E and increase RBC production during conditions that cause decreased tissue oxygenation.
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From CFU-E, pro-erythroblasts are formed. They have a large nucleus occupying most of the cytoplasm with nucleoli in it.
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The pro-erythroblasts gives rise to early (or) basophilic erythroblasts. The blue color due to the nucleus incorporates basophilic staining.
Nucleoli are absent, and the synthesis of hemoglobin (Hb) starts in this stage.
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They give rise to intermediate or poly-chromatophilic erythroblasts. Hemoglobin appears in this stage.
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Intermediate erythroblasts give rise to late or orthochromatic erythroblasts. Hb levels reach mature levels and the nucleus starts to disappear.
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With the disappearance of the nucleus, the late normoblasts become reticulocytes. At this stage, cell organelles disappear. The mitochondria are the first to disappear, followed by the ribosomes. Supravital stains are specific to stain reticulocytes.
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Reticulocytes give rise to the mature erythrocytes. The lack of a nucleus imparts them their characteristic biconcave structure, which allows them to pass through the splenic capillaries.
Author: DrV
References:
- Guyton and Hall Textbook of Physiology, 13th edition - Page no: 446 - 449
- https://www.uptodate.com/contents/regulation-of-erythropoiesis#H1
Author’s footnote
Understanding erythropoiesis is crucial to grasp the concepts behind anemia that occurs in chronic kidney disease and bone marrow failure. It is a concept that is often tested in various competitive exams and is considered a high yielding topic.
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