The stepwise production of erythrocytes is described by the figure (colour plate):
stem cells (haemocytoblast) are able to generate all types of blood cells conversion of haemocytoblast to proerythroblast is a sort of commitment that the maturation process will lead to formation of erythrocytes only under two influence of erythropoetin and the presence of nutrient factors specifically vit B12 the ribsome production is increased in the cell and the mitotic cell division occurs leading to large number of smaller sized erythroblasts (early and late ) later the haemoglobin synthesis starts on these ribosomes the synthesised haemoglobin then starts occupying the space of other organelles slow degeneration and ejection of these organelles further reduce the size of the cell to almost two third of hemocytoblast these cells are called as normoblasts later haemoglobin almost completely occupies the eytoplasmic space and ejects out the nucleus and remaining organelles finally forming a dumbbell shape (biconcave shape ) cells called reticulocytes the reticulocytes are released in blood circulation and undergo further maturation process in circulation in next two days they mature to form mature erythrocytes whole erythropoiesis requires in total about 7days to form fully mature erythrocytes from haemocytoblasts reticulocyte count in blood is a rough indicator of the rate of RBC formation
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