HEMATOLOGY 1 Lesson 3: Erythropoiesis PDF

LESSON 3: Erythropoiesis II. ERYTHROPOIESIS LECTURER: Dr. Eunice L. Estella Process of red blood cell production....

LESSON 3: Erythropoiesis II. ERYTHROPOIESIS LECTURER: Dr. Eunice L. Estella Process of red blood cell production. Dynamic process that originates from pluripotent stem LECTURE OUTLINE cells. 1 Define Erythropoiesis 2 Identify the Terms used in Erythropoiesis Normoblastic Rubriblastic Erythroblastic 3 Sequence of Erythrocyte Maturation Identify the Morphology of Red Cell Precursors and 4 Recognize their Distinguishing Features 5 Discuss the concept of Erythrokinetics I. ERYTHROCYTES (RED BLOOD CELLS) Erythroid Island on bone marrow smear ONE TRUE MAIN FUNCTION: To carry oxygen from the Lung to the Tissues where Occurrence: Typically in Erythroid Islands, of the bone 1 the oxygen is released. marrow Accomplished by attachment of oxygen to ○ Erythroid Islands– Macrophages surrounded by Hemoglobin, the major cytoplasmic component erythroid precursors in various stages of development mature RBC. A complex-regulated process for maintaining adequate numbers of erythrocytes in the peripheral blood. SECONDARY FUNCTIONS: (these are still as important although considered secondary) A. HEMATOPOIESIS 2 Returning Carbon Dioxide to the Lungs. It is the formation of all blood cellular components which 3 Buffering the pH of the blood include RBCs are derived from hematopoietic stem cells To protect these essential life functions, the mechanisms (HSC). controlling the development, production, and normal A1. HEMATOPOIETIC STEM CELLS (HSC) destruction of RBC are fine-tuned to avoid interruptions in oxygen delivery, ○ Even under adverse conditions such as blood loss with hemorrhage. A. NORMAL PERIPHERAL BLOOD SMEAR Left: Erythropoiesis; Right: Hematopoiesis Characterized by: Their ability to self-renew and differentiate into committed hematopoietic progenitors. These differentiate into multipotent progenitors (MPP) which do not have the capacity to self-renew, but can generate lineage committed progenitors including the: Cells in a Normal PBS ○ Common lymphoid progenitor In a healthy person, the erythrocytes will not be crowded ○ Common myeloid progenitor together. COMMON MYELOID PROGENITOR gives rise to: Appear as circular homogeneous discs of merely uniform size. Granulocyte-Monocyte progenitor ○ Diameter: Ranging from 6-8 micrometers Eosinophil-Basophil progenitor The center of each is somewhat paler than the periphery. Megakaryocyte-Erythrocyte progenitor (the one with circle) This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute!  HEMATOLOGY 1 | Lesson 3: Erythropoiesis A2. BURST-FORMING UNIT ERYTHROID (BFUE) Used more often in United States The earliest identifiable colony of the RBC, In the presence It has the advantage of being a of different cytokines. descriptive appearance of the cell. Produces: a large multi-clustered colony that resembles a 2. Normoblastic Normoblasts cluster of grapes containing brightly-colored hemoglobin. Terminology ○ Refers to developing nucleated ○ These colonies range from a 1 large - 16 or more cells (i.e., blasts) with normal cluster. appearance. Contains: only a few receptors for the erythropoietin. Cell cycle activity: not influenced significantly by the 3. Rubriblastic Parallels the nomenclature used for presence of exogenous erythropoietin. Terminology granulocyte development. BFUE Under the influence of: ○ Interleukin-3 (IL-3) LECTURER’S NOTES: ○ Granulocyte-Monocyte Colony Stimulating Factor The normoblastic terminology will be used throughout (GM- CSF) this discussion ○ Thrombopoietin ○ KIT Ligand - develop into the Colony Forming Unit A. THREE ERYTHROID PRECURSOR NOMENCLATURE Erythroid (CFU-E) colonies SYSTEMS A3. NORMOBLASTIC MATURATION ERYTHROBLASTIC NORMOBLASTIC RUBRIBLASTIC Proerythroblast Pronormoblast Rubriblast Basophilic Basophilic Prorubricyte erythroblast normoblast Polychromatic Polychromatic (polychromatophilic) (polychromatophilic) Rubricyte erythroblast normoblast Orthochromic Orthochromic Metarubricyte erythroblast normoblast Polychromatic Polychromatic Polychromatic (polychromatophilic) (polychromatophilic) (polychromatophilic) erythrocyte* erythrocyte* erythrocyte* Left: Normoblastic Maturation, Right: Maturation of CFU-GEMM Erythrocyte Erythrocyte Erythrocyte PRONORMOBLAST * polychromatic erythrocytes are called reticulocytes when The earliest morphological recognizable erythrocyte observed with vital stains. precursor Derived from: the Colony Forming Unit Erythrocyte B. CRITERIA USED IN IDENTIFICATION OF THE ERYTHROID (CFU-E) PRECURSORS Morphologic identification of blood cells depends on a well In the Erythrocyte Cell Line stained peripheral blood smear or bone marrow smear. There are typically 3 (occasionally, as many as 5) divisions In hematology, a modified Romanowsky stain such as with subsequent nuclear and cytoplasmic maturation of the Wright or Wright Giemsa is commonly used. daughter cells ○ The descriptions that are mentioned will be based on ○ From a single pronormoblast, 8-32 mature RBCs usually these type of stains result. The stage of maturation of any blood cell is determined by The cellular activity at each stage of the development occurs careful examination of the nucleus and the cytoplasm. in an orderly and sequential process. IV. ERYTHROCYTE NOMENCLATURE RBC = erythrocytes 3 Nomenclatures Used for Naming Erythroid Precursors Used primarily in Europe. 1. Erythroblastic Erythroblasts Terminology ○ The nucleated precursors in the Wright or Wright Giemsa bone marrow Basophilia – amount of ribosomal RNA Eosinophilia – accumulation of Hgb This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 2  HEMATOLOGY 1 | Lesson 3: Erythropoiesis Qualities of Greatest Importance in Identification of RBCs As a result, the nucleus cytoplasmic ratio decreases Nuclear chromatin pattern (texture, density, C: Nuclear chromatin pattern becomes coarser, 1 homogeneity) 3 clumped and condensed as the nucleus decreases 2 Nucleus:cytoplasm ratio (N:C ratio) more rapidly than the size of the cell. 3 Nuclear Diameter 4 Presence or absence of nucleoli 5 Cytoplasmic color V. GENERAL TRENDS IN THE MATURATION OF RBC Pronormoblast; nucleoli (inside the pink circle) Immature RBC = Pronormoblast Chromatin in the nucleus is described as “open”. As the cell matures, it becomes pyknotic. ○ meaning, darker in color Nucleoli (less dense area) ○ Represents the area where the ribosomes are formed. ○ Seen early in cell development as cells begin actively synthesizing proteins. ○ As RBC matures, the nucleoli disappear which Figure 8.2 General Trends in the Maturation of RBC persist ultimate cessation of protein synthesis. A : As red blood cells mature, several trends affect A. NUCLEUS TO CYTOPLASMIC RATIO (N:C RATIO) 1 their appearance Morphologic feature used to identify and stage RBC and Overall diameter of the cell decreases. WBC precursors​ ○ From big diameter (immature) to a small diameter (matures). RATIO Color of cytoplasm change A visual estimate of what area is occupied by the nucleus ○ From blue → gray blue → salmon pink compared with the cytoplasm​ Blueness or basophilia SUMMARY OF N:C RATIO ○ Due to acidic components that attract the basic stain such as methylene blue. If the areas of each are approx. Ratio is 1:1​ The degree of cytoplasmic basophilia correlates with equal the amount of ribosomal RNA. The proportion of the These organelles decline over the life of the If the Nucleus takes up Less nucleus is LOWER, and developing red blood cell, that is why the bluness will than 50% of the area of the cell the ratio is lower fade. 1:5 or less than 1 Pinkness, eosinophilia or acidophilia If the Nucleus takes up more the ratio is HIGHER ○ Due to the accumulation of more basic than 50% of the area of the cell e.g. 3:1 or 3 components that attract the acid stain called eosin. Eosinophilia of erythrocyte cytoplasm correlates with Pronormoblast and the nucleus are bigger than the 1 the accumulation of hemoglobin as the cell matures. cytoplasm. The cells start out as being active in protein production of ribosomes that make the cytoplasm basophilic. The transition in which the red or hemoglobin begins to mix with that of the blue and ends with a thoroughly salmon pink color. ○ Is when the ribosomes are gone and only hemoglobin remains. B : Diameter of the nucleus decreases more rapidly 2 2 Decreased N:C ratio. than the size of the cell. This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 3  HEMATOLOGY 1 | Lesson 3: Erythropoiesis Moderate amount of basophilia. No granules present. Undergoes mitosis. ○ Gives rise to 2 daughter Division Basophilic Normoblasts ○ More than 1 division is The proportion of the nucleus shrinks as the cell matures possible. and the cytoplasm increases proportionately, although Location Bone Marrow only. the overall cell diameter grows smaller. 1. Begins to accumulate the The N:C ratio decreases components necessary for VI. THE MATURATION SEQUENCE hemoglobin production​. 2. Produces proteins and enzymes Identification of the maturation sequence of the RBC. Cellular Activity necessary for: The identification of a given cell stage depends on a ○ Iron uptake preponderance of characteristics ○ Protoporphyrin synthesis ○ Although, the cell may not possess all the features of 3. ​Globin production also begins.​ the archetypal descriptions previously mentioned. The sequence starts with the most immature RBC, the Length of the stage >24 hours​ pronormoblast. 2. BASOPHILIC NORMOBLAST (Prorubricyte) 1. PRONORMOBLAST (Rubriblast) Basophilic normoblasts with chromatin condensation and deeply basophilic cytoplasm (Wright-Giemsa). A: Pronormoblast (rubriblast), bone marrow (Wright Stain) B: Electron micrograph of pronormoblast The earliest recognizable erythroid precursor Largest erythroid precursor ○ 20 micrometers in diameter Takes up much of the cell Nucleus Round to oval in shape N:C Ratio 8:1 A: Basophilic normoblast (Prorubricyte), bone marrow (Wright Stain) Present B: Electron micrograph of basophilic normoblast Nucleolus 1-2 in number Somewhat smaller, with a slightly coarser chromatin that Has a fine uniformed chromatin stains intensely. pattern. The chromatin begins to condense. ○ Somewhat more distinct and ○ This reveals clumps along the: Chromatin more intensely stained than Nucleus Periphery of the nuclear that of the myeloblast membrane Myeloblast = immature cell A few in the interior​. of the WBC series 6:1​ Nuclear Membrane Prominent ○ Moderate ratio. N:C Ratio 1 or more ○ 1⁄4 of the total cell area appears Nucleoli prominent to be cytoplasm. Dark blue color. Chromatin Stains deep Purple-Red​ Cytoplasm ○ Concentration of ribosomes. +/- ; May not be present at this Heterogenous quality. Nucleoli stage. This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 4  HEMATOLOGY 1 | Lesson 3: Erythropoiesis May be a deeper, richer blue when MURKY GRAY-BLUE / PINK & BLUE stained. ○ The FIRST stage wherein the pink Deeply basophilic color associated with stained Cytoplasm ○ Due to the abundance of RNA. hemoglobin can be seen. Cytoplasm ○ Much of this is evident as ○ Accumulation of hemoglobin polyribosomes in an electron pigmentation and noncurrent micrograph. decreasing amounts of RNA contribute to this color. Undergoes mitosis Division ○ Gives rise to 2 daughter cells. The LAST stage in which the cell is Division More than one division is possible​. capable of undergoing mitosis. Bone Marrow only. Bone Marrow (ONLY) of healthy Location Location ○ For healthy individuals. individuals. Detectable hemoglobin synthesis Cellular Activity Hemoglobin synthesis increases. occurs. Length of time 1st stage of hemoglobin synthesis​ Approximately 30 hours. Cellular Activity in this stage ○ Important to note that this occurs during the Basophilic 4. ORTHOCHROMIC NORMOBLAST (Metarubicyte) Normoblast stage. Length of time in >24 hours​ this stage After mitosis of the Basophilic Normoblast, ○ Evidence of continuing hemoglobin production becomes visible in the cytoplasm of the 2 daughter cells as polychromasia. Orthochromatic normoblast with pyknotic nucleus That is, the mixtures of the red-staining and pink-gray cytoplasm (Wright-Giemsa) hemoglobin with the blue of RNA in varying shades of gray. 3. POLYCHROMATIC (POLYCHROMATOPHILIC) NORMOBLAST (Rubricyte) (Left) Orthochromic normoblast (Right) Howell Jolly Body Completely condensed. Nucleus ○ It is pyknotic and deeply stained. N:C Ratio Low - 1:2 Polychromatophilic normoblast with light blue cytoplasm due to accumulation of Nucleolus ABSENT hemoglobin (Wright-Geimsa) Increase in the salmon pink color. It is slightly smaller than the basophilic normoblast. Cytoplasm ○ Reflecting nearly complete Occupies about half the area of the hemoglobin production. cell. Not capable of division due to Division It stains intensely. condensation of chromatin. Chromatin: Moderately condensed. Bone Marrow (ONLY) of healthy Nucleus ○ Sharply distinct from the pink Location individuals. parachromatin. Chromatin pattern varies. Hemoglobin production continues. ○ Early stage: More openness. Late stage: The nucleus is ejected ○ End: Becomes condensed. Cellular Activity from the cell. Howell – Jolly Bodies: Small Early stages: 4:1 N:C Ratio fragments of the nucleus. Late stages: 1:1 Length of time in Nucleoli ABSENT 48 hours this Stage This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 5  HEMATOLOGY 1 | Lesson 3: Erythropoiesis 5. POLYCHROMATIC (POLYCHROMATOPHILIC) ERYTHROCYTE (Reticulocyte) Erythrocyte Maturation KEY POINTS IN RBC MATURATION (Left) Reticulocyte with pink-gray cytoplasm due to residual RNA (Right) Reticulocytes at arrows, peripheral blood. Always “baseball” round. This stage the nucleus has been Nucleus Large, pale → darker, smaller → extracted. loss of nucleus. TOTALLY ABSENT. Nucleus Ruling: Becomes more condensed with ○ When a cell loses its nucleus, Nuclear chromatin age. regardless of its cytoplasmic Basophilia of cytoplasm is an appearance, it is a Reticulocyte. indicator of immaturity. Late stage: The cell is the same color As hemoglobin develops, as a mature RBC – salmon pink. cytoplasm becomes more Cytoplasm Remains larger than a red blood cell magenta or salmon pink. Shape: Irregular Cytoplasm of the red cell does not Lacks a Nucleus so the contain specific granulation. Cytoplasm Division Polychromatic Erythrocytes cannot Increase (↑) in cytoplasm divide. Cytoplasm from intensely blue (full Resides in the Bone Marrow for 1 day of RNA) → grayish (mixture of RNA or longer and then moves into the and hemoglobin) → reddish (full of Location Peripheral Blood for about 1 day hemoglobin, no RNA). before reaching maturity. Completes production of Hemoglobin N:C Ratio Decreases as the cell matures. Cellular Activity from Residual Messenger (RNA) Reduces with maturity. using the remaining ribosomes. Cell size ○ Gradually decreases. Length of time in 3 days. Nucleated red cells Are not a physiological this stage (orthochromic component of the normal peripheral normoblast) smear. 6. ERYTHROCYTE (MATURE RBC) NORMOBLASTIC SERIES: SUMMARY OF STAGE MORPHOLOGY Bone % in bone Cell or Stage Diameter N:C Ratio Nucleoli Marrow marrow Transit Time 12-20 Pronormoblast 8:1 1-2 1% 24 hr um Basophilic 10-15 6:1 0-1 1%-4% 24 hr Normoblast um Polychromatic 10-12 4:1 0 10%-20% 30 hr Normoblast um Erythrocyte (Mature RBC) Orthochromic 8-10 um 1:2 0 5%-10% 48 hr Normoblast This will circulate the peripheral blood for approximately 120 Bone Marrow No days. Polychromatic 8-10 um 0 1% 24-48 hr Nucleus Erythrocyte This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 6  HEMATOLOGY 1 | Lesson 3: Erythropoiesis (Solid Line) which declines slightly during maturation. Proteins, other than hemoglobin, predominate in early stages. Hemoglobin concentration begins to rise in the basophilic normoblast stage, reaching its peak in reticulocytes & representing most protein in more mature cells. Normoblastic Series: Stage Morphology GRAPH OF THE TRENDS IN RBC DEVELOPMENT VII. ERYTHROKINETICS Erythrokinetics Cycle Graphical Presentation of Trends in RBC Development It is the term describing the Dynamics of RBC production The graph shows the changes in cellular diameter, RNA and destruction. synthesis & content, DNA synthesis & content, protein and hemoglobin content during the RBC development. A. THE CONCEPT OF THE ERYTHRON Erythron is the collection of all stages of erythrocytes Graph Explanation throughout the body ○ It is from the Shrinks from the Developing precursors from the bone marrow RBC Diameter A pronormoblast to the Circulating erythrocytes (Solid Line) reticulocyte stage. Peripheral blood Vascular spaces within specific organs such as For protein production, it is at the spleen Rate of RNA its peak at the pronormoblast When the term Erythron is used, it conveys the concept of a B Synthesis stage and ends at the unified functional tissue (Solid Line) orthochromic normoblast This is distinguished from RBC Mass stage. ○ Erythron is the entirety of the Erythroid cells in the body ○ RBC Mass: refers to the red cells in the circulation. Correlates to stages of development that are able to 3 COMPARTMENTS/ LOCATIONS FOR RBC divide namely: 1 Peripheral Circulation Rate of DNA ○ Pronormoblast stage 2 Bone Marrow C Synthesis ○ Basophilic normoblast (Solid Line) 3 Within Organs e.g. Liver and Spleen stage ○ Early polychromatic normoblast stage Hemoglobin Dashed line represents the D Concentration total protein concentration This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 7  HEMATOLOGY 1 | Lesson 3: Erythropoiesis Erythron cycle B. ERYTHROKINETICS Function of Nephron (in the Kidneys) The role of the red blood cells is to carry oxygen WHY THE KIDNEYS? To regulate the production of red blood cells for that purpose, the body requires a mechanism for sensing The kidney receives approximately 20% of the cardiac whether there is adequate oxygen being carried to the 1 output with little loss of oxygen from the levels leaving the tissues. heart. ○ If not, RBC production and the functional efficiency This location provides early detection when oxygen levels 2 of existing red blood cells must be enhanced. decline. CONSTANT HEMOGLOBIN MASS C2. WHAT HAPPENS TO THE KIDNEYS DURING HYPOXIA? The balance between delivery of erythrocytes to the blood from the bone marrow and removal of erythrocytes from LECTURER’S NOTES: the blood results in relatively constant hemoglobin mass in Scenario: Patient has hemorrhage or hemolysis, which the circulation. brings about increased RBC destruction or other factors Increased production of erythrocytes occurs that decreases oxygen carrying capacity of the blood. ○ when oxygen transport to the tissues is impaired ○ in the state of hypoxia This would be sensed by the peritubular interstitial cells in It takes 18 to 21 days to produce a red blood cell from the the kidneys. stimulation of the earliest erythroid progenitor (BFU-E) to When there is low oxygen levels in the blood, the release from the bone marrow. peritubular interstitial cells in the kidney secrete erythropoietin. C. HYPOXIA The main stimulus to RBC production. ERYTHROPOIETIN (EPO) Detected by the peritubular cells which produce Major stimulatory cytokine for RBCs. erythropoietin. EPO production is regulated, maintaining a level of RBC Erythropoietin is the major stimulatory cytokine for red production sufficient to replace 1% of RBCs that normally blood cell production. die everyday. C1. OXYGEN-SENSING SYSTEM Mechanism that checks if there is adequate oxygen being carried to the tissues. The second feature of this system must be a mechanism for influencing the production of RBCs The primary oxygen-sensing system of the body is located in the peritubular fibroblasts of the kidneys. Erythropoietin This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 8  HEMATOLOGY 1 | Lesson 3: Erythropoiesis WHAT HAPPENS TO IMMATURE RBCs (IN THE BONE MARROW) WHEN ERYTHROPOIETIN ACTS UPON THEM? 1 They would mature into reticulocytes. They would become more available in the peripheral 2 blood. FACTORS THAT DECREASE THE O2 CARRYING CAPACITY OF THE BLOOD THAT INCREASES EPO PRODUCTION 1 Hemorrhage 2 Increased RBC destruction 3 Other factors JAK2 Signaling D. ACTION OF ERYTHROPOIETIN Erythropoietin– A true hormone produced in one location, the kidney, acting in the distant location which is the bone marrow. A growth factor or cytokine initiates an intracellular message to the developing RBCs, this process is called Signal Transduction. Hypoxia increases EPO production in Peritubular cells mainly by Transcriptional Regulation. The EPO gene has a Hypoxia sensitive region or enhancer Kidney and RBC Maturation as a regulatory component. E. 3 MAJOR EFFECTS OF EPO Allow early release of reticulocytes from the bone 1 marrow 2 Inhibition of Apoptosis 3 Reduced Marrow Transit Time The essence is that Erythropoietin (EPO) puts more RBCs into the circulation at a faster rate than occurs without its stimulation. ADDITIONAL NOTES: [NATIONAL CANCER INSTITUTE] Apoptosis is defined as “A type of cell death in which a series of molecular steps in a cell lead to its death. This is one method the body uses to get rid of unneeded or abnormal cells.” E1. EARLY RELEASE OF RETICULOCYTES Induce Changes in the Adventitial Cell Layer of the 1 Bone Marrow EPO induces changes in the sinus barrier making the Kidney Physiology bone marrow sinus barrier increase in the width of the The binding of erythropoietin, the ligand to its receptor on spaces for the RBCs to get out of the bone marrow. erythrocyte progenitor, initiates a cascade of intracellular This alone is insufficient for cells to leave the bone events termed as the Program. marrow because RBCs are held in the marrow as they ○ Ultimately leads to cell division, maturation, and more express surface membrane receptors for adhesive RBCs entering the circulation. molecules located on the bone marrow stroma. There is movement now from one compartment (bone EPO Downregulates the Expression of Surface marrow) where immature RBCs are located and are being 2 Adhesive Membrane Receptors brought into peripheral circulation where they are needed. Cells can exit the marrow earlier than cytoplasmic EPO’s effects are mediated by the Janus-Activated organelles while the mitochondria remain normal. Tyrosine Kinase 2 (JAK2) signal transducers associated with the cytoplasmic domain of the EPO receptor and ultimately affect gene expression in the RBC nucleus. This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 9  HEMATOLOGY 1 | Lesson 3: Erythropoiesis Result: is the presence in the circulation of ○ This process of intentional wastage of cells reticulocytes that are still very basophilic because they occurs by apoptosis and it is part of the cell’s have not spent much time degrading the ribosomes or genetic program. making hemoglobin as they normally would before entering the bloodstream. Evasion of apoptosis by erythroid progenitors and 2 ○ This is called The Production of Shift precursors. ​ Reticulocytes Direct EPO rescue from apoptosis​ ○ Major way in which EPO is able to increase RBC THE PRODUCTION OF SHIFT RETICULOCYTES production​ “Shift” because they have been shifted from the bone ○ When EPO binds to its receptor on a CFU-E, one marrow early. of its effects is to reduce production of the FAS It is a quick fix because it is limited in effectiveness. Ligand​ ○ Available precursors in the bone marrow are depleted in FAS: Apoptosis Induction Signal → induces several days and still may not be enough to meet the cell death​ need in the peripheral blood for more cells. FasL: expressed by more mature RBCs​ ○ In a Normal Healthy Individual: EPO levels are E2. INHIBITION OF APOPTOSIS (Apoptosis Rescue) LOW Cell production should be at a low rate Increasing the number of cells that will be able to because Hypoxia is NOT present. 1 mature into circulating erythrocytes by decreasing Excess early erythroid precursors should apoptosis (programmed death of RBC progenitors)​ undergo apoptosis​. It takes about 18-21 days to produce an RBC from stimulation of the earliest erythroid progenitor (BFUE) to E3. REDUCED MARROW TRANSIT TIME release from the bone marrow. In times of increased need of red blood cells, such as when there is loss 1 Apoptosis rescue from the circulation during hemorrhage, this time lag A major way in which EPO increases RBC mass by would be a significant problem. increasing the number of erythroid cells that survive and mature to enter the circulation. Increase the rate at which the surviving precursors can LECTURER’S NOTES: 2 enter the circulation. Imagine if you have a patient with Accomplished by two means: hemorrhage/hemolysis and you would just wait for ○ Increased rate of cellular processes 18-21 days for the bone marrow to replenish the ○ Decreased cell times red blood cells in the circulation? That would 3 Accelerated processes definitely be a problem. Hemoglobin Production Bone marrow egress with loss of adhesive receptors One way to prepare for such a need would be to Acquisition of egress-promoting surface molecules maintain a store of mature red blood cells for Cessation of Division emergencies. F. MEASUREMENT OF ERYTHROPOIETIN ○ But RBCs cannot be stored in the body for this Quantitative measurements are performed on plasma and sort of eventuality, however, because they have a other body fluids. limited life span. So again, mature red blood cells ○ Measured through Chemiluminescence. can only stay in the circulation for approx. 120 ○ Ref Int: 4-27 mU/L days. Reference intervals may differ from every Therefore, what the body does is that instead of storing laboratory, but it is usually this. mature cells for emergencies, the body produces more Increased amounts of EPO are seen in the urine of most colony forming unit erythroids (CFU-E) than needed patients with anemia. at all times. ○ Except for patients with anemia of renal disease. ○ When there is a basal or a steady state demand for red blood cells, or when everything is just G. THERAPEUTIC USES FOR ERYTHROPOIETIN: normal, the extra progenitor cells are allowed to RECOMBINANT ERYTHROPOIETIN die. Used as therapy in certain anemias. When there is an increased demand for red blood cells ○ Anemia associated with chronic kidney disease and (e.g hemorrhage, hemolysis, or any other situation with chemotherapy. an increased demand in the oxygen-carrying capacity), Used to stimulate RBC production prior to autologous the RBC progenitors have about an 8-10 day head blood donation and after bone marrow transplantation​. start in the production process. Blood Doping This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 10  HEMATOLOGY 1 | Lesson 3: Erythropoiesis ○ Banned in organized sports event. Limited capacity of the RBC to replenish ATP (energy 2 ○ Increases the RBC count and blood viscosity to source) dangerously high levels and can lead to fatal arterial and venous thrombosis​. LECTURER’S NOTES: RBC is unnucleated, does not have mitochondria, so LECTURER’S NOTES: glycolysis is through anaerobic metabolism. Unfortunately, some athletes illicitly use erythropoietin Anaerobic means there is a production of a by-product injections to increase the oxygen carrying capacity of which is lactic acid, making the pH low or acidic blood to enhance endurance and stamina. promoting iron oxidation. ○ ie. Athletes in long distance running and cycling. MEMBRANE SYSTEM RELYING ON ATP BEGIN TO FAIL OTHER STIMULI FOR ERYTHROPOIESIS Lack of ATP leads to Oxidation of Membrane Lipids and 1 Testosterone 1 Proteins. 2 Pituitary and Thyroid Hormones 2 Intracellular Sodium Increases, Potassium Decreases. VIII. ERYTHROCYTE DESTRUCTION 3 Selective Permeability of the Membrane is Lost. All cells in our body experience deterioration of their 4 Water enters the Cell. enzymes over time due to natural catabolism. The Discoid Shape is Lost and the RBC becomes 5 Most cells however are able to replenish needed enzymes Spherical. and continue their cellular processes. LECTURER’S NOTES: AS A NON-NUCLEATED CELL RBCs must remain high flexible while exiting the spleen The red blood cell however or the mature erythrocyte is by squeezing through the spleenic sieve, formed by the unable to generate new proteins such as enzymes so as epithelial cells lining the venus sinuses and the its cellular functions decline. The cell ultimately approaches basement membrane. death. When spherical RBCs are rigid and are not able to RBCs squeeze through the narrow spaces, they become The average RBC has a sufficient enzyme function to live trapped against the endothelial cells and the basement 120 days. membrane. RBCs lack mitochondria so it relies on glycolysis for ○ In this situation, if they are readily ingested by production of ATP. macrophages that patrol along the sinusoidal lining. SENESCENCE FRAGMENTATION ON INTRAVASCULAR HEMOLYSIS Process of cellular aging. (MECHANICAL HEMOLYSIS) ○ Major way in which RBCs die normally. A small portion of RBCs die by means of fragmentation on ○ Loss of glycolytic enzymes is central to this process. intravascular hemolysis or what we term as mechanical ○ Culminates in phagocytosis by macrophages. hemolysis. Occurs within the lumen of blood vessels. TWO TYPES OF RBC DESTRUCTION Intravascular rupture of RBCs from purely mechanical or Extravascular Hemolysis 1 traumatic stress results in fragmentation and release of the Macrophage-Mediated Hemolysis cell contents into the plasma. Intravascular Hemolysis 2 ○ This only happens in small amounts. Mechanical Hemolysis Proteins with roles: Haptoglobin and Hemopexin. EXTRAVASCULAR HEMOLYSIS (MACROPHAGE-MEDIATED ○ Salvage the released hemoglobin so that its iron is not HEMOLYSIS lost in the urine. So that it can be reused again for the production of Occurs in the Spleen RBCs. FACTORS THAT CONTRIBUTE TO EXTRAVASCULAR ○ Happens in cases of hemolysis. HEMOLYSIS 1 Substantial volume of blood is seen in the spleen Movement of red blood cells through the splenic pulp is sluggish. The available glucose in the surrounding plasma is depleted – Glycolysis slows down pH is low (acidic). ○ Promoted iron oxidation. This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 11