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reason..

b12 is required in dna synthesis ( remember purine and pyrimidine metab)
due to a deffn in b12 there is irregularity in the nucleus while dividing in the BM which results in hypersegmented neutrophils

same is the reason for megaloblasts.. cytoplasm increases.. but no dna synthesized so no cell division.. hence cell stuck with big cytoplasm
thus megaloblasts
 

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b12 is required in dna synthesis ( remember purine and pyrimidine metab)
due to a deffn in b12 there is irregularity in the nucleus while dividing in the BM which results in hypersegmented neutrophils

same is the reason for megaloblasts.. cytoplasm increases.. but no dna synthesized so no cell division.. hence cell stuck with big cytoplasm
thus megaloblasts
Yes, You are right for cytoplasm because DNA more impaired >>>RNA and protien synthesis.
But this mechanism for cytoplasm not for large nucleus
I think, nuclear enlargement in megaloblastic anemia b/c of either of arrest of cell cycle in S phase and cell can not progress from G2 to M phase (in this stage the cell try hardly to get over impaired DNA synthesis by making alot of polyploid(3,3.5 or even 4N) more than usuall (2N) and this lead to increase of DNA content in nucleus------ Large nucleus.
 

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Yes, You are right for cytoplasm because DNA more impaired >>>RNA and protien synthesis.
But this mechanism for cytoplasm not for large nucleus
I think, nuclear enlargement in megaloblastic anemia b/c of either of arrest of cell cycle in S phase and cell can not progress from G2 to M phase (in this stage the cell try hardly to get over impaired DNA synthesis by making alot of polyploid(3,3.5 or even 4N) more than usuall (2N) and this lead to increase of DNA content in nucleus------ Large nucleus.
I do not think this explanation works, the hypersegmentation is a consequence of impaired dna synthesis, producing more dna would not be possible. Is it possible that the neutrophils do not divide because there is not enough dna to duplicate but the cell gets "bigger" and hypersegmented anyway? or that neutrophils stay longer in circulation because they are under produced, and that hypersegmentation is a form of "aging"?
 
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