HAEMATOPOIESIS (Formation and development of blood cells)


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Haematopoiesis is the Formation and Development of the blood cells or blood cellular components. all the cells in the human body and the organ system in the human body are generally Derivatives of the stem cell.

The stem cell are of two types-

1) Embryonic stem cell

2) Tissue specific stem cell

- Embryonic stem cells can differentiate into all the cell lineages in vivo and in vitro.

- Tissue specific stem cells are undifferentiated cells. The tissue specific stem cells are found among the differentiated cells in the some organs of the body.

Blood cells including Monocyte, Erythrocytes, Lymphocytes etc. are derived from a type of cell which are called Hematopoietic stem cell (HSC). In human the site of formation and Development of blood cell or blood cellular components changes during the Embryonic development. Initially this occur inside the Yolk sac, after that in the third month of gestation period HSC become established in the liver (or Foetal liver). After that around fifth month of gestation period HSC start occurring in the spleens well as liver and by the forth to sixth month HSC start occurring in the Bone marrow.


Initial event in the haematopoiesis process include the division of stem cell into two, of which one is destined to differentiate into a specific cell type.
This New cell give rise to either a myeloid stem cell or a lymphoid stem cell and the differentiation between the lymphoid and myeloid stem cells are determined by the amount of cytokinesis. These derivatives of stem cell are now referred as now Progenitor cells because of they have loss the capacity of self renewal.
Generally lymphoid progenitor cell give ruse to T cell, B cell and Natural killer cell while Myeloid progenitor cell generates RBC, WBC ( Monocyte, Lymphocytes, Mast cells, Neutrophils etc.).
Their are various cytokines are required for maturation, Proliferation, Differentiation of different kinds of blood cell types like Colony stimulating factors (CSF), stem cell factor (SCF), Granulocyte colony stimulating factor (G - CSF) etc.

Regulation of Hematopoiesis

Hematopoiesis is regulated by variety of mechanisms, a adult tissue generally expresses a variety of factors that act to maintain both proliferation and differentiation of various cell lineages, includes soluble factors, DNA methylation, Transcription factors etc.

- DNA methylation involves the  addition of methyl group to the 5- carbon position of the cytosine ring. DNA methylation affect the expression of gene because  proteins (Regulatory proteins) binds to methylated DNA that are differ from those that bind to Un-methylated DNA. The DNA methylation take place in the Eukaryotes.

- Soluble factors that regulate differentiation include those molecules that binds to cell surface receptors, such as Fibroblast growth factor, Granulocytes colony stimulating factor, Interleukins etc.

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