Haematopoiesis PDF

# Haematopoiesis ## Definition: This is the formation of blood cells. Haematopoiesis have different sites of formation. The site are 1. The yolk sac (mesoderm) 2. Liver (Hepatic) 3. Bone marrow (Myeloid) ## Sites of blood cell formation ### Mesoblastic period (2 months) In the first two months of f...

# Haematopoiesis ## Definition: This is the formation of blood cells. Haematopoiesis have different sites of formation. The site are 1. The yolk sac (mesoderm) 2. Liver (Hepatic) 3. Bone marrow (Myeloid) ## Sites of blood cell formation ### Mesoblastic period (2 months) In the first two months of foetal life, haematopoiesis occurs in the clusters of mesodermal cells of the embryonic yolk sac known as the blood islands. ### Hepatic period (2-6 month) Within the next four months the liver is the major site, hence it is called the hepatic period, but the spleen makes some contribution in the production of lymphocytes and red cells. ### Myeloid phase (6 months/armonth) At this period the bone marrow starts production of blood cells and becomes the major site of formation of most cells right up to birth. During this period the lymph nodes and thymus gland are important site for the production of lymphocyte and monocytes. ### Extrauterine Haematopoiesis During the first five years, myeloid haematopoiesis occurs practically all the bone marrow. Thereafter, there is a progressive replacement of the blood forming marrow in the long bones. The rest occurs in the bones of the trunk (vertebrate ribs, sternum scapulae, pelvis and the skull). ### Extreamedullary Haematopoiesis In some disease conditions, the marrow supply of blood cells falls short of demand, and blood cell formation resumes in locations outside the bone marrow such as liver and spleen. This is known as extramedullary haematopoiesis. # HAEMATOPOIESIS: DEV. ORIGIN OF BLOOD CELLS AND STIMULATORS ## Uncommitted bone marrow Pluripotent (Multipotential) stem cell (hemocyboblast) | Stimulator | | |:---|:---| |FLT-3 | | |TNF-a| | |TGF-BI | Committed Bone marrow, Lymphocyte stem cell | |IL-2 | | |IL-7 | Common lymphoid progenitor | |IL-12 | | |SDF-1 | | - Bone marrow B cells - Thymus T cells | Stimulator | | |:---|:---| |IL-2 | | |IL-4 | | |IL-6 | | |IL-7| | |GSF | Common myeloid progenitor | |SDF-1 | | | Stimulator | Committed Erythrocyte stem cell | |:---|:---| |SCF | | |EPO | | |IL-3 | | |GM-CSF | | | Stimulator | Committed neutro Phil/monocyte stem cell | |:---|:---| |SCF | | |M-CSF | | |G-SCF | | |GM-CSF | | |IL-3 | | | Stimulator | Committed Basophil stem cell | |:---|:---| |SCF | | |G-CSF | | |IL-3 | | |GM-CSF | | | Stimulator | Committed Easinophil stem cell | Committed Stem cell for megakaryocyte | |:---|:---|:---| |IL-3 | SCF | |IL-5 | G-CSF | |GM-CSF | IL-3 | |GM-CSF | IL-6 | | Cell Type | |:---| |Redcell | |Neutrophil/monocyte | |Basophil | |Eosinophil | |Megakaryocyte | |Platelete | ## Key to stimulators - SCF - stem cell factor - TPO - Thrombopoietin - IL - interleukon - GM-CSF - Granulocyte Macrophage-colony stimulating factor - EPO - Erythropoietin - M-CSF - Macrophage - Colony stimulating factor - G-CSF - Granulocyte-Colony stimulating factor - SDF-1 - stromal cell-derived factor-1 - FLT- - Fris like tyrosine kinase 3 - TNF-a - Tumour necrosis factor - alpha - TGF B - Transforming growth factor beta ## Developmental Origins of Blood Cells Scientifically, it is believed that all blood cells originated from pluripotent or multipotent stem cell also known as hemacytoblast, which actively divide and differentiate into committed stem cells when stimulated by some specific hormones or ligands destined to lead to the production of a particular blood cell type, red, white or platelet. The Chart in Fig 1 and 2, summarized the origin and development of blood cells. The committed stem cells when stimulated actively divide and their offspring differentiate further into the earliest discernible mature forms of the particular blood cell which are still actively mitotic and are called the “blast” cells. The main changes, which characterize the progressive transformations of the “blast” cells into the mature non-dividing forms seen in the circulation are: 1. a decrease in mitosis 2. a decrease in cell size 3. disappearance of nucleoli 4. nuclear chromatin becomes coarser 5. RNA decreases 6. specific cytoplasmic inclusions appear for cells that have them (Hb in red cells, granules in granulocytes).