Hematopoiesis Immunology / Formation of Blood cells / Immunology Kuby

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Hematopoiesis
Hematopoiesis is the formation and development of red and white blood cells from a type of cell called the hematopoietic stem cell (HSC). Hematopoietic stem cells are self-renewing, that is they can multiply constantly to maintain their number. Primitive hematopoiesis wherein, the embryo produces only red blood cells that can provide developing organs with oxygen, begins in the embryonic yolk sac. As the embryo continues to develop, the hematopoiesis process moves to the liver, the spleen, and bone marrow. Later, after birth, hematopoiesis stops in the liver and spleen and continues in the bone marrow. Generally, in normal adults, hematopoiesis occurs in the bone marrow and is called medullary hematopoiesis. In certain pathological conditions, hematopoiesis occurs in the liver and spleen and is known as extramedullary hematopoiesis.
Hematopoietic stem cells are pluripotent or multipotent, which means, they can differentiate into various other cell types. Early in hematopoiesis, a multipotent stem cell differentiates giving rise to either a common lymphoid progenitor cell or a common myeloid progenitor cell. These progenitor cells do not have the capacity for self-renewal and are committed to a particular cell lineage. Common lymphoid progenitor cells give rise to progenitors of B and T- lymphocytes, natural killer cells, and some dendritic cells. B lymphocyte progenitors later differentiate into B cells and T lymphocyte progenitors differentiate into T helper cells and T cytotoxic cells. Common myeloid progenitor cells give rise to progenitors of red blood cells, granulocyte-monocyte progenitors, megakaryocyte, progenitors of eosinophils, basophils, mast cells, and dendritic cells. When the appropriate growth factors and cytokines are present, progenitor cells proliferate and differentiate into the corresponding cell type. Progenitors of RBC give differentiates into RBC, Granulocyte-monocyte progenitors give rise to monocytes and neutrophils, megakaryote differentiates into platelets, eosinophil progenitor differentiates into eosinophil, and basophil progenitor differentiates into basophil.
The hematopoietic cells grow and mature in bone marrow on a meshwork of stromal cells, which are nonhematopoietic cells that support the growth and differentiation of hematopoietic
cells by providing a hematopoietic-inducing microenvironment.
Each of the blood cells produced by hematopoiesis has a characteristic life span and then dies by programmed cell death. White blood cells have the shortest life span, sometimes surviving just a few hours to a few days, while red blood cells can last up to 120 days or so. If programmed cell death fails to occur, a leukemic state may develop with uncontrolled growth of white blood cells in the body.
Hematopoiesis is a constant process that produces a massive number of cells. In a typical day, the body might produce 200 billion red blood cells, 10 million white blood cells, and 400 billion platelets.

References
Kelly, J., 1992. Immunology: by Janis Kuby, WH Freeman.