Hematopoiesis: Red Blood Cell and Bone Marrow

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The formation and development of the cells of the blood.

It is a continuous regulated process of blood cell production that includes cell renewal, proliferation, differentiation and maturation.

It is the process by which immature precursor cells develop into mature blood cells. The currently accepted theory on how this process works is called the monophyletic theory which simply means that a single type of stem cell gives rise to all the mature blood cells in the body. This stem cell is called the pluripotential (pluripotent) stem cell.

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• Hematopoiesis in the fetal liver reaches its peak by the third month of development. • The developing spleen, kidney, thymus and lymph nodes contribute to the process.

• Thymus is the first fully developed organ and becomes the major site of the T cell production.

• KIDNEY & SPLEEN – produce B cells.

• In this phase, megakaryocyte production begins. The spleen gradually decreases granulocytic production & involves itself solely in lymphopoiesis. Detectable levels of hemoglobin may be shown.

Medullary Phase . Myeloid Phase

• It begins in the 5th month of fetal development. Hematopoiesis begins in the developing bone marrow cavity

• Medullary hematopoiesis occurs. It occurs in the medulla or inner part of the bone marrow

• Mesenchymal cells (embryonic tissue) migrate into the core of the bone & differentiate into skeletal & hematopoietic blood cells. Hematopoietic activity, esp. myeloid activity is apparent

• 3:1 (myeloid: erythroid) by 21 weeks of gestation 6th month – bone marrow is the main site of Hematopoiesis

The M:E ratio or Myeloid:Erythroid ratio describe the ratio relationship of the granulocyte line of cells to the erythrocyte line of cells. Normally there are from 25% to 35% of the bone marrow cells of the erythroid line. There are then
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