Hemopoiesis PDF

Hemopoiesis By Dr. Sara Samir Sadoon Hematopoiesis Is the process by which blood cells are formed due to their limited life span. All blood cells are derived from a common stem cell in red bone marrow which is called pluripotential hemopoietic stem cell. Sites of hemopoiesis In th...

Hemopoiesis By Dr. Sara Samir Sadoon Hematopoiesis Is the process by which blood cells are formed due to their limited life span. All blood cells are derived from a common stem cell in red bone marrow which is called pluripotential hemopoietic stem cell. Sites of hemopoiesis In the embryo ! hemopoiesis initially occurs in the yolk sac and later in the liver, spleen, and lymph nodes. After birth ! hemopoiesis continues almost exclusively in the red marrow of different bones (in the newborn, all bone marrow is red). Stem cells Are pluripotential cells that can divide continuously and whose daughter cells form specific , irreversibly differentiated cell types. Reside in the bone marrow Give rise to all mature blood cells The daughters of stem cells (myeloid and lymphoid progenitor cells), can commit to any of the alternative differentiation pathways by undergoing numerous divisions that leads to the production of one or more specific types of blood cells ,but they can not self- renew. Myeloid stem cells Give rise to 1. Erythrocytes 2. Eosinophils 3. Neutrophils 4. Basophils 5. Monocytes 6. Megakaryocytes. Lymphoid stem cells Some ! remain in the bone marrow ,proliferate, mature, and become B lymphocytes. Others ! leave the bone marrow and migrate via the blood stream to lymph nodes and the spleen, where they proliferate and differentiate into B lymphocytes. Other undifferentiated lymphoid cells ! migrate to the thymus gland, where they proliferate and differentiate into T lymphocytes. Both B and T lymphocytes reside in numerous peripheral lymphoid tissues, lymph nodes, and spleen. Erythropoiesis Stages of development : A-immature red cell precursors : 1-proerythroblast 2-basophilic erythroblast B-mature red blood precursor cells : 3-polychromatic erythroblast 4-orthochromatic erythroblast 5-polychromatophilic erythrocyte (reticulocyte) 6-erythrocyte  The earliest recognizable erythroid precursor seen in the bone marrow is large basophilic staining cell. Contains a single large well defined, rounded nucleus, ribosomes, mitochondria and golgi apparatus As the early precursor cell matures. nucleus increases in size. cell becomes smaller. more eosinophilic indicating hemoglobin. During intermediate stages of maturation, cytoplasm becomes polychromatic indicating mixture of basophilic proteins and eosinophilic hemoglobin.  Further maturation, hemoglobin synthesis continue and cytoplasm becomes entirely eosinophilic. Late stages of maturation 1. hemoglobin is abundant 2. Few mitochondria and ribosomes are present 3. Nucleus is small dense and well circumscribed. Proerythroblast first erythrocyte precursor produced directly from myeloid stem cell. They are characterized by ❑ their size ❑a very dense nuclear structure (large nucleus ) ❑narrow layer of cytoplasm (basophilic cytoplasm ). Basophilic erythroblast a strongly basophilic cytoplasm a condensed nucleus. Smaller than proerythroblast The basophilia of these two cell types is caused by the large number of polyribosomes involved in the synthesis of hemoglobin. Polychromatic erythroblast Also called intermediate normoblast. Last precursor cell capable of mitosis. Smaller than basophilic erythroblasts Cytoplasm appears greyer because of presence of haemoglobin. Orthochromatic erythroblast Also called late normoblast. Incapable of cell division the nucleus continues to condense Polychromatophilic erythrocyte Also called reticulocyte (because the clustering of ribosomes forms a reticular network). It’s formed when the nucleus is extruded from the normoblast. Can carry oxygen and enter the blood stream found in low concentrations in normal blood. Erythrocyte (RBC) The final product of erythropoiesis released from bone marrow into the circulation production of erythrocytes is regulated by (EPO) Erythropoietin is a glycoprotein hormone. If blood oxygen concentration falls, the release of erythropoietin rises. embryonic life until early neonatal life ! Produced in the yolk sac, liver and kidney. In the adult ! produced only in the kidneys. Granulopoiesis Committed myeloid stem cells differentiate into three types of cells, neutrophils, Basophils and eosinophils A- immature white cell precursors : 1-myeloblasts 2-promyelocytes B- partly mature white cell precursors : 1-myelocytes 2-metamyelocytes C-mature neutrophils: 1-band cells 2-segmented neutrophils  Myeloblasts The least mature cells in the granulocyte lineage. round –to –ovoid cells. Mononuclear with fine reticular nuclear structure narrow layer of basophilic cytoplasm without granules Promyelocyte Are the product of myeloblast division. larger than their progenitor cells. Nucleus is eccentric. Wide layer of basophilic cytoplasm Myelocytes Are direct product of promyelocyte mitosis. Smaller than their progenitors. Ovoid nucleus. Cytoplasm relatively basophilic Metamyelocytes Produced from final myelocyte division. unable to divide ,from this stage ,only further maturation of the nucleus occurs. Nucleus slowly take on a kidney –bean shape. Band cells Represent further development of metamyelocytes. The beginnings of segmentation may be visible, but the constriction should never cut more than two –thirds of the way across the nucleus. Segmented neutrophils represent final stage in the lineage. Nuclear segments are connected by narrow chromatin bridges. Cytoplasm is soft pink to colorless. Thrombopoiesis Megakaryocytes differentiate from myeloid stem cell and are responsible for production of platelets. Three stages of maturation of megakaryocytes 1-Basophilic stage, megakaryocyte is Small has diploid nucleus abundant basophilic cytoplasm. 2.Granular stage the nucleus is more polypoid cytoplasm is more eosinophilic and granular  3.Mature stage, megakaryocyte is very large with approx 16-32 nuclei abundance of granular cytoplasm. It undergoes shedding to from platelets. Megakaryocytes -Reside in bone marrow. -Cytoplasm with granules is pinched off from megakaryocytes to form thrombocytes. Thrombopoietin is a glycoprotein hormone produced mainly by liver and kidney regulates the production of platelets in bone marrow by stimulation of the production and differentiation of Megakaryocytes Production of monocyte The monoblast is a committed progenitor cell that is identical to the myeloblast in its morphology. Further differentiation leads to the promonocyte a large cell a basophilic cytoplasm a large, slightly indented nucleus. Promonocytes divide twice in the course of their development into monocytes.  Mature monocytes enter the bloodstream, circulate for about 8 hours, and then enter the connective tissues, where they mature into macrophages and function for several months. Lymphopoiesis It is probable, that all lymphocyte progenitor cells originate in the bone marrow. Some of these relatively undifferentiated lymphocytes migrate to the thymus, where they acquire the attributes of T lymphocytes.  Other bone marrow lymphocytes remain in the marrow, differentiate into B lymphocytes, and then migrate to peripheral lymphoid organs where they inhabit and multiply in their own special compartments. The first identifiable progenitor of lymphoid cells is the lymphoblast, a large cell capable of dividing two or three times to form prolymphocytes. B –cell Found in bone marrow ,then differentiate into B-cells. --Maturation culminates in migration of B –lymphocytes to other lymphoid organs and tissues (e.g, spleen ,liver ,tonsils ,lymph nodes). proliferate and differentiate into plasma cell (antibodyforming cells ) T –CELL Leaves the bone marrow and settles in thymus ,to produce thymocyte. Enter the blood stream and migrate to specific regions of peripheral lymphoid organs Then thymocytes differentiate into :- 1. -T-helper 2. -T-cytotoxic 3. -T-memory 4. -T-suppressor Thanks