Formation of Blood Cells

Hemopoiesis (also hematopoiesis) is the developmental process of the formed elements. Shortly after conception an embryo begins the process in the yolk sac. Afterwards, the developing fetus shifts the process to the liver, spleen, thymus and lymph nodes. 3 months before birth the process shifts yet again to bone marrow, which becomes the principle source of hemopoiesis throughout life.

The highly vascularized red bone marrow resides primarily in bones of the axial skeleton, pectoral and pelvic girdles, as well as the proximal epiphyses of the humerus and femur.

Pluripotent stem cells are mesenchymal cells representing less than .1% of RBM cells having the ability to develop into several other kinds of cells. These further lead to 2 other stem cells known as Myeloid and lymphoid stem cells.

Myeloid Stem Cells lead to development of:

RBCs (erythrocytes) (CFU-E)

Platelets (thrombocytes)

Eosinophils

Neutrophils (CFU-GM)

Basophils

Of the cell types listed above, all except eosinophils and basophils are produced by intermediate or Progenitor cells before fully developing.

Lymphoid Stem Cells lead to the development of T and B lymphocytes (T/B cells).

HGFs (Hemopoietic Growth factors) control the production of progenitor cells. Examples include erythropoietin (EPO) and Thrombopoietin (TPO). EPO cells are produced in the kidneys, therefore, renal failure contributes to insufficient production of RBCs. TPO originates in the liver to promote the synthesis of platelets from Megakaryocytes
Cytokines - Typically acting as autocrines/paracrines, cytokines are glycoproteins synthesized by RBM cells, leukocytes, macrophages, fibroblasts and endothelial cells. They promote the spread of progenitor cells.

2 Cytokine Families that stimulate production of WBCs:

CSFs (Colony-Stimulating Factors)

Interleukins

Medical uses of HGFs

In response to diminished/defective blood cell synthesis, recombinant DNA technology has advanced to develop recombinant (hybrid) erythropoietin, also known as Epoetin alfa, to treat low RBC concentration during end-stage kidney disease. Patients going through chemotherapy are treated with Granulocytic-Machrophage CSF and Granulocyte CSFs to treat low WBC concentration. Thrombopoietin is used to treat platelet depletion.