W1 Hematopoiesis (Reid, H) PDF

Histology: HEMATOPOIESIS / HEMOPOIESIS Dr. Herman Reid Professor, Department of Medical Foundations Office Hours: By appointment: [email protected] LEARNING OBJECTIVES By the end of this lecture, the student should be able to … 1) Explain where blood cells are produced at different stages of deve...

Histology: HEMATOPOIESIS / HEMOPOIESIS Dr. Herman Reid Professor, Department of Medical Foundations Office Hours: By appointment: [email protected] LEARNING OBJECTIVES By the end of this lecture, the student should be able to … 1) Explain where blood cells are produced at different stages of development 2) List the two types of bone marrow and the basic structure of bone marrow 3) Explain how a single type of multipotential stem cell gives rise to two lineages (myeloid cells and lymphocytes), and then each of those two lineages gives rise to all the mature blood cells 4) List the stages of each lineage of blood cell development and what happens in each stage. *You will NOT be expected to recognize each stage visually, but you will be expected to know the characteristics of the cells at each stage of development. *You will be responsible for knowing what happens at each stage of erythropoiesis, granulocytopoiesis, monocytopoiesis, thrombopoiesis, and lymphocytopoiesis 5) Explain the general effects of growth factors on blood cell development 2 HEMATOPOIESIS (AKA: HEMOPOIESIS) poeisis Gr. “to make” hema Gr. “blood” Definition: the process of blood cell formation from established blood cell precursors • Mature blood cells have a relatively short life-span, must be continuously replaced by the progeny of stem cells • After birth, production of new blood cells occurs in the bone marrow • Under normal conditions, the production of blood cells can adjust rapidly to the needs of the body, increasing several-fold in a short time • In a healthy adult person, approximately 1011 - 1012 new blood cells are produced daily in order to maintain steady state levels in the peripheral circulation 1012= one trillion ** One single type of hematopoietic stem cell (HSC) in the bone marrow gives rise to all the formed elements of blood two lines lymphoid linegives rise to all the lymphocyes Note: In this lecture we will use the terms MULTIPOTENTIAL and HEMATOPOIETIC to mean the same. myeloid linegives rise to everything but lymphocytes (erythrocytes, platelets, neutrophils, eosinophils, basophils, monocytes; also mast cells) 4 REVIEW THE DEFINITION OF A STEM CELL Of the two daughter cells produced when a stem cell divides1) One daughter remains a stem cell 2) One daughter goes on to terminally differentiate *This keeps an available population of stem cells always Hemopoiesis Blood cells in the adult: formed in red bone marrow red cells granulocytes monocytes lymphocytes platelets Lymphocytes are also formed in the lymphatic tissues We will study blood cells in smears (cytology) and biopsies (histology) of bone marrows, and then compare ! 6 Hemopoiesis In fetus, red & white cells formed in several organs (before bone marrow is formed) 1st / yolk-sac phase - begins 3rd week of gestation blood islands form in walls of yolk sac of the embryo 7 Hemopoiesis ▪ 2nd / hepatic phase - early fetal development - hemopoietic centers appear in the liver - during the 2nd trimester the liver is the major blood forming organ in the fetus 8 Liver without and with hematopoiesis - Note the differences !! What is extramedullary hematopoiesis ? Hemopoiesis ▪ 3rd / bone marrow phase - bone marrow (and other lymphatic tissue involved) - begins during 2nd trimester of pregnancy - after birth hematopoiesis takes place in red bone marrow and lymphatic tissues 10 Bone marrow with hematopoiesis - images 11 Review: Differentiate bone marrow from blood smears ! This is the appearance of normal bone marrow smear at high magnification. Note the presence of an eosinophilic myelocyte, a basophilic myelocyte, and a plasma cell (later slides will explain these appearances) The red blood cells here are normal, happy RBC's. They have a zone of central pallor about 1/3 the size of the RBC. The RBC's demonstrate minimal variation in size (anisocytosis) and shape (poikilocytosis). A few small fuzzy blue platelets are seen. In the center of the field are a band neutrophil on the left and a segmented neutrophil on the 12 right. BONE MARROW • One of the largest organs of the body • Main site of hematopoiesis in adults • Bone marrow is considered a type of connective tissue * * Bone marrow is found in: 1) Cavities in spongy/trabecular/cancellous bone 2) In the medullary/bone marrow cavity of the diaphysis 13 TWO TYPES OF BONE MARROW EXIST BASED ON THEIR APPEARANCE 1) RED BONE MARROW Color is produced by the presence of blood and blood - forming cells 2) YELLOW BONE MARROW Color is produced by the presence of a great number of adipocytes 14 NEW BORN - ALL MARROW IS RED As the child grows, most of the bone marrow changes gradually into the yellow variety 25 - YEAR OLD: RED MARROW IS CONFINED TO CANCELLOUS BONE: The proximal quarters of the long bones (femurs, humeri), skull bones, ribs, sternum, scapulae, clavicles, vertebrae, pelvis and upper half of the sacrum BUT - in response to severe blood loss, yellow bone marrow can become red bone marrow at any time in life • Yellow bone marrow is “seeded” by blood-borne hematopoietic cells 15 RED BONE MARROW HAS 2 COMPONENTS: STROMA AND SINUSOIDS 1) STROMA Where the blood cells develop “LAND” 2) SINUSOIDS Blood vessels where the mature blood cells enter the blood stream ”SEA” 16 1) STROMA: • 3-dimensional meshwork of reticular cells (also called adventitial cells, but are basically fibroblasts) and a delicate web of reticular fibers containing hematopoietic cells, macrophages, and a few adipocytes. ➢ Reticular cells • Secrete reticular fibers composed of type III collagen • Send cytoplasmic projections outward (away from basal lamina of endothelial cells), These touch projections of other reticular cells; forms a 3-D network surrounding discrete hemopoietic cords (islands) **Remember that reticular fibers are argyrophilic (silver loving) **Remember that this reticular cell and fiber network is THE supporting mesh in soft tissues such as ✓ Liver ✓ bone marrow See c.t LECTURE ✓ the tissues and organs of the lymphatic system - spleen, lymph nodes • Stroma of bone marrow contains fibers and ground substance like other connective tissues: ✓ collagen types I and III ✓ fibronectin ✓ laminin ✓ proteoglycans • Laminin and fibronectin and others interact with cell receptors (integrins) to bind developing cells to the reticular fibers in the stroma • When developing cells are mature and ready to enter bloodstream, they inactivate their integrins and release from the meshwork Compare with the previous diagrams ! 18 2. SINUSOIDS 2nd COMPONENT OF RED BONE MARROW • Formed by sinusoidal capillaries (most sources call these sinusoidal capillaries; a few sources call them venous sinuses) • Lined by endothelial cells sitting on a discontinuous basal lamina * Sinusoids are where RBCs, WBCs, and platelets enter the circulation after their production in the bone marrow. Which other organs contain sinusoids / sinusoidal capillaries ? 19 BONE MARROW with hematopoiesis 20 Section of Red Bone Marrow showing some of Its components. Six blood sinusoid capillaries containing many erythrocytes are indicated by arrowheads. Note the thinness of the blood capillary wall. Giemsa stain. Medium magnification. 21 Hematopoiesis – General Overview Review ! Note: Although the specific pathways / steps may differ … the end results are essentially the same ☺ 22 Blood Cell Lifelines RBC: 7-8 days maturation in marrow 120 days in circulation Lymphocyte T cell: 2-3 days maturation in marrow Days to decades in circulation Monocytes: 2-3 days maturation in marrow Most 16 hours; some years in circulation Neutrophils: About 2 weeks maturation in marrow 6-8 hours in circulation Eosinophils: About 2 weeks maturation in marrow 8-12 hours in circulation Basophils: About 2 weeks maturation in marrow 9-18 months in circulation Platelets: 5 days maturation in marrow 10 days in circulation 23 ERYTHROPOIESIS 24 GENERAL TRENDS IN THE DEVELOPMENT OF ERYTHROCYTES • Cell gets smaller • Nucleus condenses, eventually extruded • Gradually loses ribosomes, mRNA, and organelles • Gradually gains hemoglobin From first recognizable (proerythroblast) to release into bloodstream takes ~7 days 25 1) PROERYTHROBLAST -large cell, basophilic cytoplasm, visible nucleoli (comes from CFU-E which is not morphologically distinguishable) 2) BASOPHILIC ERYTHROBLAST-strongly basophilic cytoplasm, no visible nucleoli. Basophilia of #1 and #2 is caused by the large number of polyribosomes involved in the synthesis of hemoglobin 3) POLYCHROMATOPHILIC ERYTHROBLAST -During this stage, polyribosomes decrease, and areas of cytoplasm begin to be filled with hemoglobin which is acidophilic. Thus, this stage 26 cell stains both colors (basophilic and acidophilic) ID both ? ID all ? 4) ORTHOCHROMATOPHILIC ERYTHROBLAST (Normoblast) -Nucleus continues to condense, lose evident basophilia (but not quite all polyribosomes) resulting in uniform acidophilia 5) RETICULOCYTE (polychromatophilic erythrocyte) -After it expels its nucleus, becomes a reticulocyte. Still has a few polyribosomes that aggregate (when treated with dye cresyl blue) to form a stained “reticular” network. **reticulocyte leaves the bone marrow and passes into the bloodstream 6) ERYTHROCYTE (RBC) -The mature form, has lost all polyribosomes 27 EM of RETICULOCYTE (polychromatophilic erythrocyte) - note fimbriated cytoplasmic processes after nucleus extrusion - mitochondria and endosomes still present **NEARLY ALL ERYTHROCYTES ARE RELEASED INTO THE CIRCULATION(AS RETICULOCYTES) AS SOON AS THEY ARE FORMED ***BONE MARROW IS NOT A STORAGE SITE FOR ERYTHROCYTES Blood smear stained with cresyl blue to show reticulocytes (arrows) Reticulocytes are about 1-2% of RBCs in bloodstream, 28 % can increase after blood loss Note erythrocyte maturation and release into circulation RETICULOCYTES in peripheral blood showing POLYRIBOSOMES 29 HEMATOPOIETIC GROWTH FACTORS See “Cytokines” lecture • All are secreted proteins that bind to receptors on their target cells • Control the rates of hematopoiesis of stem cells (can have other functions as well) Erythropoietin (EPO): synthesized by cells in the kidney Students-EPO is the only growth factor on this table you need to, remember - for now.. 30 ERYTHROPOIETIN (EPO) • Synthesized and secreted by the kidney in response to decreased blood oxygen concentration • Acts on receptors on surface of CFU-E (in bone marrow) (ErP Erythrocyte Progenitor) • **Renal failure patients on dialysis were universally anemic before the advent of commercial EPO; they required transfusions • EPO is also (illegally) sometimes used as a blood doping agent in endurance sports such as bicycle racing, triathlons and marathon running. (Tour de France !) 31 **2019 Nobel Prize in Medicine 32 Kinetics of Erythropoiesis RBCs have life span of 120 days At 4 months of age RBCs become senescent (old) Within the macrophage system of the spleen, liver and bone marrow - phagocytosis and degredation of senescent RBCs occurs Spleen Liver RBC breakdown Jaundice / Icterus An abnormal increase of bilirubin in circulation may result in jaundice / icterus ! - yellowing of tissues and urine. Causes for the abnormal increase in unconjugated and conjugated bilirubin are varied. (pathology lectures) GRANULOCYTOPOIESIS GRANULOCYTOPOIESIS - development of granulocytes (neutrophils, basophils, and eosinophils) From the neutrophil, eosinophil and basophil progenitor cells 5/6 morphological stages occur (influenced by cytokines) Myeloblasts, promyelocytes, myelocytes, metamyelocytes, band cells → mature neutrophils or eosinophils or basophils. 37 GRANULOCYTOPOIESIS MYELOBLAST Looks like lymphocytes, but often has 3-5 prominent nucleoli PROMYELOCYTE Azurophilic (non-specific) granules appear MYELOCYTE Oval or flat nucleus Specific granules appear; Last stage at which cell division is possible 38 GRANULOCYTOPOIESIS METAMYELOCYTE Specific granules continue to accumulate, Nucleus indented, c or v shape BAND/STAB CELL Eosinophil and basophil stab cells exist but are rarely found, mainly band cells are immature neutrophils mature NEUTROPHILS EOSINOPHILS BASOPHILS39 “SHIFT TO THE LEFT” • • • Increased number of immature neutrophils in the bloodLarge number of band cells appear in the blood. Called a “shift to the left” **indication of bacterial infection. ***UNLIKE ERYTHROCYTES, MATURE AND NEAR-MATURE NEUTROPHILS ARE STORED IN BONE MARROW • Ratio of these neutrophils in bone marrow to bloodstream is ~5:1 • This reserve pool can be released abruptly into the circulation in response to inflammation, infection, or strenuous exercise Note the band neutrophils, metamyelocytes, and myelocytes Origin of “SHIFT TO THE LEFT” referring to increase in immature neutrophils in blood Looking at a blood smear stained with Wright stain; 41 doing a differential WBC count TODAY ! Most modern, urban medical labs have an automated hematology analyzer In addition to counting, measuring and analyzing red blood cells, white blood cells and platelets, automated hematology analyzers also measure the 42 amount of hemoglobin. MONOCYTOPOIESIS - Note that monocytes and granulocytes share the same progenitor (GFU-GM) 43 MONOCYTOPOIESIS PROMONOCYTE (Monocyte progenitor) Cytoplasm is bluish and houses numerous azurophilic (non-specific) granules (lysosomes) MONOCYTE Every day, the average adult forms more than 10 billion monocytes, most of which then enter the circulation Within a day or two, the newly formed monocytes enter the connective tissue spaces of the body and transform into MACROPHAGES LYMPHOPOIESIS 45 DEVELOPMENT OF LYMPHOCYTES Hematopoietic stem cells Myeloid stem cell CFU-GEMM Lymphoid stem cell CFU-L Some migrate to thymus where they become T lymphocytes, then they migrate to populate specific regions of peripheral lymphoid organs (more on T cell development in the thymus in the “Lymphoid tissue” lecture) Some differentiate into B lymphocytes within the bone marrow and then migrate to peripheral lymphoid organs Note: actually, B cells do not completely develop until after they leave bone marrow 46 DEVELOPMENT OF LYMPHOCYTES - review 47 LEUKEMIAS • • Leukemias are malignant clones of leukocyte precursors They occur in lymphoid tissue (lymphocytic leukemias) and in bone marrow (myelogenous and monocytic leukemias) • In these diseases, there is usually a release of large numbers of immature cells into the blood • Leads to a lack of some cell types and excessive production of others (which are often abnormal in function) • Patient is usually anemic and prone to infection For more, see Pathology lectures In contrast to aplastic anemia, leukemia results in a highly cellular marrow. The marrow between the pink bone trabeculae seen here is nearly 100% cellular, and it consists of leukemic cells of acute lymphocytic leukemia (ALL) that have virtually replaced or suppressed normal hematopoiesis. Thus, though the marrow becomes quite cellular, there can be peripheral cytopenias. This explains the complications of leukemia including infection (lack of normal leukocytes), hemorrhage (lack of 48 platelets), and anemia (lack of red blood cells). Myelogenous leukemias At high power, the bone marrow of a patient with acute myelogenous leukemia is seen here. There is one lone megakaryocyte at the right center. Here is a view of a peripheral blood smear in a patient with CML. (Chronic Myelogenous Leukemia) Often, the numbers of basophils and eosinophils, as well as bands and more immature myeloid cells (metamyelocytes and myelocytes) are increased. Unlike AML, there are not many 49 blasts with CML. Multiple Myeloma Round lesions filled with a soft reddish material are indicative of foci of myeloma in this section of vertebral bone. In this bone marrow biopsy section at medium power, there are sheets of plasma cells of multiple myeloma that are very similar to normal plasma cells, but the cells may also be poorly differentiated. Usually, the plasma cells are differentiated enough to retain the function of immunoglobulin production. The lucencies seen here in the vertebral column are the result of multiple myeloma. The lucent areas are filled with plasma cells. This patient had back pain. 50 THROMBOPOIESIS origin of platelets 51 THROMBOPOIESIS - The nucleus becomes highly polyploid, it contains up to 30 times as much DNA as a normal cell (chromosomes replicate but the cell doesn’t divide) – (ENDOMITOSES – under the influence of thrombopoietin) - Giant cell, invaginations of plasma membrane form demarcation membranes with platelet granules inside each. Note: Demarcation membranes / platelet demarcation channels 52 These break off to form platelets Platelets do not contain nuclei, but they do contain granules that contain: TEM note peripheral cytoplasm of megakaryocyte with platelet demarcation channels ✓ platelet-derived growth factor ✓ fibroblast growth factor ✓ von Willebrand factor (which promotes adhesion of platelets to endothelial cells) ✓ platelet factor IV (which stimulates blood coagulation) 53 THROMBOPOIESIS • In adults, platelets originate in the red bone marrow by fragmentation of the cytoplasm of mature megakaryocytes • Megakaryocytes arise by differentiation of megakaryoblasts • Each megakaryocyte produces between 5,000 and 10,000 platelets Megakaryocytes form thin processes that cross the wall of the sinusoid and fragment at their tips, liberating the platelets ◼ Note: megakaryocytes in bone marrow 55 HOW RBCS AND WBCS ENTER BLOODSTREAM FROM MARROW RBCs • Because erythrocytes (unlike leukocytes) do not have sufficient motility to cross the wall of the sinusoid, they are believed to enter the sinusoid by a pressure gradient that exists across its wall • In red bone marrow, veins leaving are smaller than arteries entering, creates pressure “suction” that “sucks” mature RBCs from stroma into capillary. WBCs • Leukocytes, after the action of releasing substances, cross the wall of the sinusoid by their own activity (diapedesis in reverse) 56 Note: **Granulocytes never divide again In contrast, monocytes/macrophages and lymphocytes have the potential for further division. 57 Metastases to the bone marrow Seen here is a metastasis from a carcinoma to the vertebral bone marrow. Metastatic prostatic adenocarcinoma to marrow is the best example of this process. AE-1 is a cytokeratin marker for carcinomas. Seen here are nests of positively staining cells in bone marrow. This is metastatic adenocarcinoma. The marrow spaces between the trabecular bone are filled with cohesive clusters of dark blue cells and smaller groups of these cells replacing normal hematopoietic cells. This is metastatic carcinoma. The primary site in this case was breast. A bone scan can help to identify metastases. A bone marrow biopsy can confirm the diagnosis. 58 END OF THE HEMATOPOIESIS LECTURE ! Further reading if desired and reference: Junquiera’s Basic Histology Chapter 13 “Hemopoiesis”