Hematopoiesis PDF

Hematopoiesis Dr. Heba Kalbouneh DDS, MSc, DMD/PhD Professor of Anatomy, Histology and Embryology  Blood Cell Formation (Hematopoiesis) Mature blood cells have a relatively short life span and must be continuously replaced with new cells from precursors developing during hemo...

Hematopoiesis Dr. Heba Kalbouneh DDS, MSc, DMD/PhD Professor of Anatomy, Histology and Embryology  Blood Cell Formation (Hematopoiesis) Mature blood cells have a relatively short life span and must be continuously replaced with new cells from precursors developing during hemopoiesis/ hematopoiesis (Gr. haima, blood + poiesis, a making). Early embryo Yolk sac mesoderm Second trimester Developing liver and spleen Third trimester Bone marrow Dr. Heba Kalbouneh After birth, all blood cells originate in bone marrow Bone marrow The red bone marrow is a highly cellular structure that is located in the medullary cavities of the bone It consists of: Hemopoietic stem cells (the origin of different blood cells) surrounded by numerous macrophages and sinusoidal capillaries and supported by a reticular tissue. Extramedullary As the individual ages and becomes an hematopoiesis refers to the adult, the hematopoiesis that occurs in red marrow is found primarily in the organs other than bone axial skeleton (flat bones of the skull, marrow. sternum and ribs, vertebrae, and pelvic (fetal development, normal bones). The remaining bones, primarily immune responses, and the long bones in the limbs of the body, pathological circumstances) Dr. Heba Kalbouneh gradually accumulate fat, and their marrow becomes yellow. Consequently, Under certain conditions they lose the hemopoietic functions. (severe bleeding or hypoxia), yellow marrow reverts to red Dr. Heba Kalbouneh Macrophage Discontinuous Basement membrane Continuous capillary Sinusoidal capillary Endothelium Intercellular gap Sinusoid Reticular cell Reticular tissue forming the stroma of the bone marrow Reticular Dr. Heba Kalbouneh fiber  Between the hematopoitetic cells run the sinusoids, which have discontinuous endothelium, through which newly differentiated blood cells and platelets enter the circulation Sinusoids Hematopoitic cells Dr. Heba Kalbouneh Red marrow is also a site where older, defective erythrocytes undergo phagocytosis by macrophages, which then reprocess heme-bound iron for delivery to the differentiating erythrocytes.  Hematopoietic stem cell (Pluripotent) Stem cells Myeloid stem cell Lymphoid stem cell (Multipotent) GEMM (Multipotent) Progenitor cells (Commited, unipotent stem cells) CFU-E CFU-M CFU-G CFU-M CFU-Ls NK Lymphoblast B Lymphoblast T Lymphoblast Megakaryoblast Erythroblast Monoblast Myeloblast Precursor cells Mature cells  Stem cells are capable of asymmetric division and self-renewal. Stem cells can maintain the original Precursor cells produce only population mature blood cells Erythroblasts are precursor cells Stem Erythroblast cell Stem cell Dr. Heba Kalbouneh Every time the stem cell multiplies, it will give All Erythroblasts multiply and two cells, one differentiates into mature RBCs differentiate into mature RBCs and the other cell adds to the original (erythrocytes) and no erythroblasts are population left in the end Hematopoietic pluripotent stem cells Stem cells and progenitor cells cannot be morphologically distinguished and resemble large lymphocytes Myeloid stem cells Lymphoid stem cells Rate of cell division: Slow in Stem cells Rapid in progenitor and precursor cells Progenitor cells/ CFUs All progenitor cells (CFUs) produce precursor cells (or blasts) Precursor cells/ Blasts Selected precursors of different blood cells Dr. Heba Kalbouneh Precursor cells gradually assume the morphologic characteristics of the mature, functional cell types they will become  Pluripotent hematopoietic stem cells All blood cells arise from a single type of stem cell in the bone marrow called pluripotent stem cell It can produce ALL BLOOD CELL TYPES It proliferates and forms two major cell linages Myeloid stem cells Lymphoid stem cells Progenitor and precursor cells Progenitor and precursor cells Granulocytes -Neutrophils Dr. Heba Kalbouneh -Basophils -Eosinophils Erythrocytes T lymphocyte Megakaryocytes B lymphocyte Monocytes Natural killer cells  Pluripotent hematopoietic stem cells Myeloid stem cells Lymphoid stem cells CFU Erythrocyte CFU-E Progenitor cells/ CFUs CFU Lymphocytes CFU Monocyte CFU-Ls CFU Granulocyte- CFU-M Monocyte CFU-GM CFU Granulocyte CFU-G CFU Megakaryocyte CFU-M The progenitor cells for blood cells are often called colony-forming units (CFUs), because they give rise Dr. Heba Kalbouneh to colonies of only one cell type when cultured in vitro or injected into a spleen.  Blood Cell Formation (Hematopoiesis) Throughout childhood and adult life, erythrocytes, granulocytes, monocytes, and platelets continue to form from stem cells located in bone marrow Important & required Erythropoiesis: the process which produces erythrocytes Granulopoiesis: the process which produces granulocytes Thrombopoiesis: the process which produces thrombocytes Lymphopoiesis: the process which produces lymphocytes Monocytopoiesis: the process which produces monocytes Dr. Heba Kalbouneh  Cytoplasmic maturation Nuclear maturation Proerythroblast Erythropoiesis (red cell formation) ✓ Takes about 1 week ✓ Rate is controled by the hormone erythropoietin (secreted by the kidney cells) Basophilic and the availability of iron, folic acid, erythroblast vitamen B12, protein precursors Polychromatophilic Stages of differentiation are characterized by: erythroblast 1- Decreasing cell size 2- Progressive loss of organelles Presence of free ribosomes at early stages Normoblast Accounts for the marked cytoplasmic basophilia (blue) Reticulocyte 3- Progressive increase in hemoglobin content Dr. Heba Kalbouneh Accounts for increasing eosinophilia Erythrocyte (pink/red)  ✓The first recognizable erythrocyte precursor Proerythroblast ✓Largest cell (17um) ✓Large pale nucleus with prominent nucleolus ✓Pale basophilic cytoplasm ✓The cell becomes smaller (15um) ✓Nucleus: smaller and darker Basophilic ✓Deeply basophilic cytoplasm (high in ribosomes) erythroblast ✓The cell becomes smaller (13um) ✓Nucleus: smaller and darker Polychromatophilic ✓Cytoplasm becomes violet erythroblast ✓(takes basic (ribosomes) and acidic stains (Hb) Normoblast ✓The cell becomes smaller (11um) (Acidophilic ✓Nucleus: smaller, darker and eccentric to be expelled outside erythroblast!!!) ✓Cytoplasm is acidophilic (Hb) The nucleus is extruded at this stage Reticulocyte ✓Immature erythrocyte but slightly larger (9um) Dr. Heba Kalbouneh ✓No nucleus ✓Cytoplasm is acidophilic (Hb) but contains remnants of ribosomes forming reticulum Erythrocyte ✓Can be stained by supravital stains (brilliant cresyl blue) Reticulocytes Are immature red blood cells (last stage) The cell has extruded its nucleus, but is still capable of producing hemoglobin Supravital dye: precipitation of reticulum in the cytoplasm (brilliant cresyl blue) Normally, only about 1% of all red blood cells in the bloodstream are reticulocytes They circulate for about 1-2 days before developing into mature red blood cells An increase in reticulocytes ---- blood loss (hemorrhage) Granulopoiesis (Neutrophils, Eosinophils and Basophils formation) ✓ Takes about 2 weeks Stages of differentiation are characterized by: 1- Cytoplasmic changes dominated by synthesis of azurophilic granules and specific granules. Dr. Heba Kalbouneh First, formation of the azurophilic granules (similar in all three types of granulocytes) Second, formation of the specific granules (differ in each of the three types of granulocytes) 2- Condensation, indentation and segmentation of the nucleus Dr. Heba Kalbouneh Dr. Heba Kalbouneh Myeloblast ✓The first recognizable precursor Promyelocyte ✓The largest (20um) ✓Azurophilic granules start to appear Myelocyte ✓3 types Neutophilic Eosinophilic Basophilic ✓The cell becomes smaller ✓ The nucleus becomes smaller and darker ✓ Specific granules start to appear Metamyelocyte ✓3 types ✓Cannot divide ✓Undergoes metamorphosis ✓Nucleus becomes indented (kidney shaped) ✓Specific granules increase in number Band cell (stab cell) ✓3 types ✓Nucleus becomes curved rod in shape  Neutrophilic band cells (important) Their percentage does not exceed 5% in peripheral blood Band cell is almost a mature neutrophil, just doesn’t have a segmented The appearance of large numbers of immature neutrophils nucleus yet (band cells) in the blood, sometimes called a “shift to the left,” is clinically significant, usually indicating a bacterial infection. This means that the bone marrow has been signaled to release more neutrophils and increase production of neutrophils Neutophil Eosinophil Basophil Dr. Heba Kalbouneh  Myeloblast Promyeloctye Bone marrow pool Myelocyte Metamyelocyte Band cell Neutrophil Circulating pool Marginating pool Dr. Heba Kalbouneh  Developing and mature neutrophils exist in four functionally and anatomically defined compartments: (1) The granulopoietic compartment in active marrow (2) Storage as mature cells in marrow until release (3) The circulating population (4) A population undergoing margination Margination is a process in which neutrophils adhere loosely and accumulate transiently along the endothelial surface in venules and small veins. Dr. Heba Kalbouneh Note: Margination of neutrophils in some organs can persist for several hours and is not always followed by the cells’ emigration from the microvasculature.  At sites of injury or infection, neutrophils and other granulocytes enter the connective tissues by migrating through intercellular junctions between endothelial cells of postcapillary venules in diapedesis. Inflamed connective tissues thus form a fifth terminal compartment for neutrophils, where the cells reside for a few days and then die by apoptosis, regardless of whether they have performed their major function of bacterial phagocytosis. Changes in the number of neutrophils in the blood must be evaluated by taking all their compartments into consideration. Thus, neutrophilia (an increase in the number of circulating neutrophils) does not necessarily imply an increase in granulopoiesis. Intense muscular activity or the administration of epinephrine can cause neutrophils in the marginating compartment to move into the circulating compartment, producing neutrophilia even though granulopoiesis has not increased. However, glucocorticoids (adrenal hormones) such as cortisone increase the mitotic activity of neutrophil precursors and this also increases the blood count of neutrophils. Dr. Heba Kalbouneh How many RBCs are in 1 ul of peripheral blood? 5 million/ul How many WBCs are in 1 ul of peripheral blood? 4500-11000/ul But in the bone marrow (myeloid tissue)!!! Myeloid: Erythroid 3:1 Remember the life span!!!!! Dr. Heba Kalbouneh  White blood cell abnormalities Increased numbers of white cells appear in the peripheral blood in a variety of disorders and provide a useful clue to the underlying disease. A considerable and sustained increase of circulating neutrophils in bacterial infection An increase of circulating eosinophils in parasitic infection and some allergies Dr. Heba Kalbouneh Bone marrow Apirate or biobsy Needed to diagnose disorders like aplastic anemia or leukemia Bone marrow transplantation In bone marrow diseases like leukemia, hematopoietic stem cells taken from a donor are infused into the same or another person Dr. Heba Kalbouneh Thrombopoiesis Hematopoietic pluripotent stem cell Myeloid stem cell Colony forming unit- megakaryocyte Dr. Heba Kalbouneh Megakaryoblast Promegakaryocyte Megakaryocyte Monocytopoiesis Hematopoietic pluripotent stem cell Myeloid stem cell Colony forming unit- monocyte Dr. Heba Kalbouneh Monoblast Promonocyte Monocyte  Hematopoietic pluripotent stem cell Lymphopoiesis Lymphoid stem cell Extra note: some consider this progenitor cell as multipotent While some consider that we Lymphocyte colony forming cell have 2 or 3 different progenitor cells Dr. Heba Kalbouneh NK Lymphoblast T Lymphoblast Directly into blood Thymus B Lymphoblast T Lymphocyte Natural killer lymphocyte BM B Lymphocyte  Band cell Polychromatophilic (Neutrophil) Basophilic erythroblast myelocyte Proerythroblast Mature erythrocytes Neutrophilic Dr. Heba Kalbouneh metamyelocyte Eosinophilic metamyelocyte Mature Eosinophilic neutrophil myelocyte Neutrophilic Mature Eosinophil myelocyte Basophilic Normoblast erythroblast Megakaryocyte Platelets Bone marrow (Giemsa stain)  Normoblasts Polychromatophilic Megakaryocte erythroblasts Sinusoid Myelocyte Adipocyte Metamyelocyte Dr. Heba Kalbouneh Basophilic erythroblast Reticular cell Eosinophilic Myelocyte Bone marrow (H&E)  Hemopoietic growth factors (colony-stimulating factors (CSF) or cytokines) are glycoproteins that stimulate proliferation of progenitor and precursor cells and promote cell differentiation and maturation within specific lineages. Erythropoietin Thrombopoietin CSF-G Dr. Heba Kalbouneh Cloning of the genes for several important hematopoietic growth factors has significantly advanced study of blood formation and permitted the production of clinically useful factors for patients with hemopoietic disorders.  In which of the following cells involved in erythropoiesis does hemoglobin synthesis begin? a. Orthochromatic erythroblast b. Polychromatophilic erythroblast c. Reticulocyte d. Basophilic erythroblast e. Proerythroblast  Which of the following can be used to describe megakaryocytes? a. Multinucleated b. Formed by fusion of haploid cells c. Precursors to bone marrow macrophages d. A minor but normal formed element found in the circulation e. Possess dynamic cell projections from which one type of formed element is released Which cytoplasmic components are the main constituents of the dark precipitate that forms in reticulocytes upon staining with the dye cresyl blue? a. Golgi complexes b. Hemoglobin c. Nucleoli d. Nuclear fragments e. Polyribosomes  Which process occurs during granulopoiesis but not during erythropoiesis? a. Cells lose their capacity for mitosis b. Euchromatin content increases c. Nucleus becomes increasingly lobulated d. Overall cell diameter decreases e. Overall nuclear diameter decreases What fate often awaits granulocytes that have entered the marginating compartment? a. Undergo mitosis b. Crossing the wall of a venule to enter connective tissue c. Cannot reenter the circulation d. Differentiate into functional macrophages e. Begin to release platelets What is the earliest stage at which specific granulocyte types can be distinguished from one another? a. Myelocyte b. Band form c. Reticulocyte d. Metamyelocyte e. Promyelocyte  Which cell type is capable of further mitosis after leaving the hemopoietic organ in which it is formed? a. Basophil b. Eosinophil c. Reticulocyte d. Lymphocyte e. Neutrophil  Shortly after her birth a baby is diagnosed with a mutation in the erythropoietin receptor gene which leads to familial erythrocytosis (familial polycythemia). During the seventh to ninth months of fetal development, the primary effect on her red blood cell production was in which of the following? a. Liver b. Yolk sac c. Spleen d. Thymus e. Bone marrow  A 54-year-old man presents with recurrent breathlessness and chronic fatigue. After routine tests followed by a bone marrow biopsy he is diagnosed with lymphocytic leukemia. Chemotherapy is administered to remove the cancerous cells, which also destroys the precursor cells of erythrocytes. To reestablish the erythrocytic lineage, which of the following cells should be transplanted? a. Reticulocytes b. Orthochromatophilic erythroblasts c. Megakaryoblasts d. Basophilic erythroblasts e. Metamyelocytes  A smear of blood from a 70-year-old leukemia patient reveals a larger than normal population of cells that have large, round nuclei with 1 or 2 nucleoli. The cytoplasm of these cells shows azurophilic granules. Which of the following forms of leukemia would you suspect? a. Promyelocytic leukemia b. Basophilic leukemia c. Lymphoblastic leukemia d. Stem cell leukemia e. Eosinophilic leukemia