Bone Marrow Structure & Hemopoiesis PDF

# Bone Marrow Structure & Hemopoiesis ## By Dr. Amal Abd El-Hafez, Associate Professor of Histopathology ## Learning objectives * Describe the histological structure of bone marrow * Define hematopoiesis and the regulating growth factors * Describe the steps of erythropoiesis and related cellular...

# Bone Marrow Structure & Hemopoiesis ## By Dr. Amal Abd El-Hafez, Associate Professor of Histopathology ## Learning objectives * Describe the histological structure of bone marrow * Define hematopoiesis and the regulating growth factors * Describe the steps of erythropoiesis and related cellular changes * Mention the cellular changes during granulopoiesis, monopoiesis and thrombopoiesis ## Hematopoiesis= Hemopoiesis The process of production of mature blood cells from their precursors. * **Origin:** Pluripotent stem cells in bone marrow. * **Pluripotential stem cells give:** * **Common lymphoid precursor:** Starts in bone marrow, migrates to the thymus, lymph nodes,spleen and other lymphoid tissues > lymphocytes * **Common myeloid precursor:** myeloid cells (granulocytes, monocytes, erythrocytes and megakaryocytes) ## Growth factors of Hematopoiesis or Hematopoietins Substances and hormones that affect blood cell development and production. **Includes:** 1. **Stem cell factor** 2. **Granulocyte colony stimulating factor (G-CSF)** 3. **Monocyte (M-CSF)** 4. **Granulocyte/monocyte (GM-CSF)** 5. **Interleukin 3 (IL-3), IL-5, IL11 - Immune system's messengers** 6. **Erythropoietin (EPO) - hormone stimulates production of RBC in bone marrow** 7. **Thrombopoietin - hormone stimulates production of platelets in bone marrow** ## Bone Marrow [BM] A tissue specified for blood cell development and production. * **Site:** * Medullary canals of long bones * Cavities of spongy (cancellous) bones * **Types:** * **Red BM (Red Marrow):** Red in color due to blood and blood-forming cells, mainly in axial skeleton. * **Yellow BM (Yellow Marrow):** Yellow in color due to increased adipose cells * **In early intrauterine life, hematopoiesis takes place in the yolk sac and liver.** * **In newborns, all bone marrow is red, active in the production of blood cells** * **In adults, most of the bone marrow is yellow, inactive.** ## Red Bone Marrow Red BM is composed of: 1. **Stroma:** reticular fibers + reticular cells + macrophages + collagen types I and III + hemonectin (substance that bind cells to the stroma) 2. **Hematopoietic cords:** formed of developing blood cells 3. **Sinusoidal capillaries.** **Functions of Red BM:** 1. Production of all blood cells 2. Destruction of old red blood cells [RBCs] 3. Storage of iron. ## Bone Marrow Failure *Aplastic anemia* 1. **Blood disorder characterized by pancytopenia** ie., reduced the count of all the blood cells. 2. **Clinically, the patient suffers from bruises, bleeding (thrombocytopenia), repeated infection (leukopenia), lethargy, and fatigue (anemia).** 3. **Treatment:** Bone marrow transplantation (hemopoietic stem cell transplant which may be autologous or allogeneic). ## Bone Marrow Transplantation 1. **What is the aim?** 2. **Who is the donor?** 3. **What is the procedure?** 4. **What diseases can be treated?** ## Erythropoiesis The process of development and production of erythrocytes (RBCs) in the bone marrow. **Stages:** 1. **Pro-erythroblast** 2. **Normoblast** 3. **Reticulocyte** 4. **Erythrocyte** **Erythropoiesis is stimulated by: Erythropoietin, a hormone produced by the kidneys** ### Morphological changes during erythropoiesis * **Cell volume decreases** * **Nuclei:** becomes dense, decreases in size, extruded from the cell. * **Mitochondria, ribosomes and all organelles disappear** * **Amount of hemoglobin increases and fills the cell.** ## Granulopoiesis The process of development and production of granulocytes (neutrophil, eosinophil, basophil) in the bone marrow. **What are the involved growth factors?** **Stages:** 1. **Myeloblast** 2. **Promyelocyte** 3. **Myelocyte** 4. **Metamyelocyte** 5. **Band cell** 6. **Segmented cell** ### Morphological Changes: 1. **Myeloblast:** Large + open chromatin 2. **Promyelocyte:** azurophilic (primary) granules 3. **Myelocytes:** specific (secondary) granules 4. **Metamyelocyte:** indented nucleus + increased specific granules 5. **Stab or band neutrophil, eosinophil, basophil:** horseshoe nucleus + increased specific granules 6. **Mature neutrophil, eosinophil, basophil:** segmented nucleus + cytoplasmic granules according to cell type. ## Lymphopoiesis The development and production of lymphocytes. 1. **All lymphocyte stem cells originate in the bone marrow.** 2. **Some lymphocyte stem cells migrate to the thymus, to give T lymphocytes** 3. **Others give B lymphocytes in the bone marrow** 4. **Others differentiate to Natural Killer (NK) or cytotoxic T cells** 5. **They circulate between lymphoid organs and connective tissue via blood** ### Stages: 1. **Lymphoblast:** a large cell 2. **Prolymphocytes:** smaller cell with condensed chromatin 3. **Mature (small) B or T lymphocyte:** have specific cell-surface antigens detected by immunohistochemistry. 4. **B lymphocytes mature to plasma cells which produce antibodies** ## Monocytopoiesis The Formation of monocytes in bone marrow. **Stages:** 1. **Monoblast:** is the cell of origin for monocytes 2. **Promonocyte:** a large cell + indented nucleus + basophilic cytoplasm (rough endoplasmic reticulum + Golgi complex) 3. **Mature blood monocytes:** contain fine azurophilic granules (lysosomes), secretory granules 4. **In the connective tissues, monocytes mature into macrophages** ## Thrombocytopoiesis The process of mutation and production of blood platelets from megakaryocytes in bone marrow. * **Site:** Platelets originate in the red bone marrow by fragmentation of the cytoplasm of mature megakaryocytes. **Stages:** 1. **Megakaryoblast** 2. **Megakaryocyte** 3. **Platelets** ## Recommended References - **Wheater's Functional Histology: A Text and Colour Atlas**, 6th Edition - ISBN-13: 978-0702047473 - ISBN-10: 0702047473 - **The histology tutor:** - http://www2.yvcc.edu/histologyzoomer/HistologyTutorials/histology_tutorials.htm