Erythrocytes Presentation PDF

Erythrocy tes Assoc. Prof. Menizibeya Welcome Osain MD, MMedSci, Ph.D  Clinical Case Mrs. O.K., a 38 year old civil servant, was involved in a road traffic accident that resulted to significant loss of blood (over 15% of total blood volume). On admission...

Erythrocy tes Assoc. Prof. Menizibeya Welcome Osain MD, MMedSci, Ph.D  Clinical Case Mrs. O.K., a 38 year old civil servant, was involved in a road traffic accident that resulted to significant loss of blood (over 15% of total blood volume). On admission, her vital signs were unstable (BP – 50/40mmHg; PR – Non-recordable; RP – 34cpm). Vital signs following fluid resuscitation with 1 litre of normal saline : BP – 80/60mmHg; PR – 120bpm; RP – 28cpm. Urgent laboratory test was requested for Hb, PCV, blood grouping and cross-matching. Retrieved investigation results showed the following : Hb – 8 g/dl, PCV – 35%, Blood group – O positive. What Outline Introduction Hematopoietic origin of RBCs – Erythropoiesis Structure and functions of RBCs RBC indices Major transport protein of RBCs – Hemoglobin Applied physiology : Anemia  Introduction Erythrocytes, also known as Red Blood Cells (RBCs), are the most numerous, highly specialized blood cells, whose main function is to transport oxygen (O2) from the lungs to the tissues and carbon dioxide (CO2) from the tissues to the lungs Mature RBCs do not have nuclei and cytoplasmic organelles. That is why RBCs cannot synthesize proteins or lipids Energy expenditure is very low and oxygen consumption is low Use less than 2% of the total transported gas ATP formation is due to anaerobic glucose oxidation. General schema of hematopoiesis Hematopoietic origin of RBCs – Erythropoiesis 1 Erythropoiesis is the production of erythrocytes 2 The yolk sack is the first site of generation RBC precursors By week 8, the liver becomes the only source of 3 erythrocytes until the 18th week of gestation Afterwards, the spleen and bone marrow take over 4 as the leading sites of RBC production, but a small percentage of hepatic erythropoiesis remains until postnatal week 6 Under normal condition, the bone marrow remains 5 the only site of RBC generation in an adult Approximately 3 × 105 erythrocytes are produced per second in a 70-kg adult human. This suggests a huge regenerative ability of the adult bone marrow. Production of mature RBC from pluripotent stem cells Pluripotent stem cell Multipotent progenitor CFU-GEMM (colony-forming unit granulocyte erythroid monocyte and megakaryocyte) IL-3, GM-CSF, G- CSF BFU-E (burst-forming unit erythroid) IL-3, IL-9, IGF-1, GM- CSF, EPO CFU-E (colony-forming unit eryhtroid) Hb EPO accumulation (Erythropoietin) Pro-normoblast (Pro-erythroblast) Basophilic erythroblast Polychromatic erythroblast Orthochromatic erythroblast Reticulocyte Mature red blood Erythropoietin – The Main Regulator of Erythropoiesis Reduction in Hb level stimulates the production of erythropoietin from the cells of the peritubular capillary bed of the kidney cortex Erythropoietin is a hormone that serves as the main regulator of erythropoiesis The hormone is released into circulation and transported to the red bone marrow, where it stimulates the bone marrow stem cells The result is increased production of erythroid cell line. Life Span of RBCs Worn out RBCs are sequestered to the spleen, where macrophages engulf ~90% of the RBCs. ~10% is lost due to intravascular hemolysis The life span of RBCs is about 3-4 months (~120 days) A stimulated hematopoietic stem cells will pass through several intermediate stages to produce mature RBCs after 24- 36 hours. Structure of RBC RBCs are non-nucleated biconcave discs with a diameter of 7 - 8 μm and volume of 80 - 100 femtoliters (fl). Mature RBCs possess plasticity – the ability of reversible deformation. This allows them to pass through the vessels with a smaller diameter. This 7-8 μm deformability is due to the interaction between membrane proteins (glycophorin, Band 3) and cytoplasm (spectrin, ankyrin). The process of aging of RBCs is accompanied by an irreversible aggregation of spectrin and hemoglobin, which causes distortion of the RBC structure (from discocytes to impart spherocytes). Size of RBC Glycophorins hydrophilic properties to the outer surface of RBCs and electric (zeta) potential. That is why RBCs repel each other in plasma. This property of  1 2 The glycophorins (as Some plasma well as the glycolipids, membrane proteins glycoproteins of the also function as plasma membrane) can transporters, and ion function as antigens channels Red Blood Cell Indices RBC Indices Include 1. RBC count 2. Erythrocyte sedimentation rate (ESR) 3. Hematocrit (Packed cell volume, PCV) 4. Mean Corpuscular Volume (MCV) 5. Mean Corpuscular Hemoglobin (MCH) 6. Mean Corpuscular Hemoglobin Concentration 7. Color(MCHC) Index (CI) 8. Reticulocyte count Red Cell Indices RBC Count Reference values for females RBC count is a 4.2–5.4*1012/l (4.2– hematologic 5.4*106mm3) parameter that [about 4-5 million cells per involves the cubic millimeter] Reference values for calculation of males the number of 4.6–6.2*1012/l (4.6– red blood cells. 6.2*106mm3) [about 4-6 million cells per cubic N/B: The values in the bracket are in millimeter] conventional units; the values outside the Abnormal Increase and Decrease in RBC Count 1 Polycythemia (Erythrocytosis) Increase in RBC count above the upper limit of the normal value 2 Anemia (Erythrocytopenia) Reduction in the value of RBCs below the reference value Erythrocyte Sedimentation Rate (ESR) This is the rate of settling of blood devoid of clotting factors. Normal values of ESR Adult male: 1-10 mm / h Adult females: 2-15 mm / h Neonates: 1-2 mm / h Elderly: 1-20 mm / h. Factors Affecting ESR Number of RBCs 1 Size of RBCs 2 Plasma proteins 3 Level of bile pigment 4 Pathological conditions 5  Physiological/Pathological Increase and Decrease in ESR Increase in ESR Autoagglutination ESR is higher in females than in males (this (rouleaux is due to the lower number of RBCs in formation) females) Macrocytes – Pregnancy RBCs are larger Fasting (heavier) Post-vaccination (due to the increase in Hemolysis – plasma globulin and fibrinogen level) destruction of the Aging RBCS (decreased Anemia (due to rouleaux formation) cell number) Infections, inflammation and malignant Alcoholic liver conditions (cancer) – due to increased plasma disease  Physiological/Pathological Increase and Decrease in ESR Decrease in ESR Increase in perspiration (during high temperature) Mountain or highland dwellers and climbers Newborns Protein abnormalities [e.g. hypofibrinogenemia, hypogammaglobulinemia – occur in massive blood transfusion, liver failure, disseminated intravascular coagulopathy (DIC), post-cardiac surgery, liver transplantation surgery] Red cell disorders: Polycythemia, spherocytes or crenated RBCS – inhibit rouleaux formation Microcytes – smaller RBCs – decreased surface area (RBCs  ESR and the zeta potential of RBCs The zeta (ζ) potential is a repulsive force that is generated by the negative charge on RBC membrane. The negative charge is due to the presence of carboxyl group in sialic acids of the glycoproteins of the RBC membrane. The negatively charged surface creates a repulsive electric ζ potential between the RBCs – which prevents clumping (aggregation). Clumping occurs when the aggregation force is greater than the force of repulsion. Increase in RBC count can cause an increase in the Schematic representation of zeta ζ potential of the cells, which in turn will lead to a potential. Heloise Pöckel decrease in ESR. Fernandes, Carlos Lenz Cesar, and Maria de Lourdes Barjas-Castro. Electrical properties of the red blood cell membrane and Rouleau (plural, rouleaux) Rouleau (roo’low) is an aggregate of RBCs stacked like a pile of coins. The formation of rouleau indicates an increase in plasma immunoglobulins – which are responsible for bridging the membranes of RBCs. Rouleaux formation Hematocrit (Hct) Hct is the proportion, by volume, of RBCs in whole blood, expressed as a percentage. Hct is also known as packed cell volume (PCV) or Erythrocyte Volume Fraction (EVF). Plasma forms 55% and RBCs If blood is collected in a form 45% of the total blood. hematocrit tube with a suitable anticoagulant and centrifuged The thin layer of white buffy for 30 minutes at a speed of coat located between plasma 3000 revolutions per minute and RBCs contains WBCs and (rpm), the RBCs settle down at platelets. the bottom, and plasma  Factors Affecting PCV PCV decreases in: PCV increases in: Anemia Dehydration Liver diseases (e.g. Polycythemia: An increase in cirrhosis) the number of red blood cells Pregnancy (polycythemia) is normal for Chronic hemorrhage persons living at high altitudes (e.g. vaginal bleeding due (physiological polycythemia), to ectopic pregnancy i.e. but in most of the population it pregnancy due to indicates disease (polycythemia implantation of fertilized vera). Polycythemia vera – egg in locations other than excessive production of RBCs the uterine wall) by the bone marrow.  Mean Corpuscular Volume (MCV) MCV is the average volume of RBCs and it is expressed in femtoliters (fL). Normal MCV is approx. 80-90 fL. When MCV is normal, the RBC is called a normocyte. When MCV increases, the cell is known as a macrocyte and when it decreases, the cell is called microcyte. ean Corpuscular Hemoglobin Concentration (MCHC) MCHC is the concentration of hemoglobin in one RBC. It is the amount of hemoglobin expressed in relation to the volume of one RBC. Normal value of MCHC is 34±2 g/dl (30-38%). When MCHC is normal, the RBC is normochromic. When the MCHC decreases, the RBC is termed hypochromic. Mean Corpuscular Hemoglobin (MCH) MCH is the quantity of hemoglobin present in one RBC. It is expressed in pictogram (pg). Normal value of MCH is 27-32 pg.  Color Index (CI) CI is the ratio of the percentage of Hb and the percentage of RBCs in the blood. Normal CI is 1.0 (0.8– 1.2). Reticulocyte Count The reticulocyte count is a measure of the number of young red blood cells in the peripheral blood (Normal reticulocyte count: 0.5-1.5% or approx. 1- 2% (50-100x109/L). Red cell distribution width (RDW) RDW is a test that measures variation in RBC size. The normal RDW level is 10.2-14.5%. A value above the upper limit means that the RBCs significantly vary in size – known as anisocytosis. The RDW test is used together with MCV. A high RDW, with high MCV is suggestive of folate and vitamin B12 deficiency anemia If RDW is high, but MCV is not, the anemia is likely an iron- deficiency anemia. Functions of RBCs Transport function RBCs carry O2 and CO2 (respiratory function), nutrients (proteins, carbohydrates etc.) and biologically active substances to and from different cells of the body. Protective function Participate in immune reactions due to the presence of certain glycoproteins and glycolipids that possess the properties of antigens Regulatory function Maintain the acid-base balance (blood pH): Hb can bind CO2 to reduce the content of H2CO3 in the blood Hemoglobin (Hb) 1 The most abundant protein in RBC (constitute 98% of the mass of RBC cytoplasm) 2 The main carrier of blood gasses 3 The red color of RBCs is due to the presence of this protein 3 When RBC has completed its life span, Hb binds to the plasma protein, haptoglobin, and the resulting complex is captured and destroyed by phagocytic cells of the liver and spleen. During massive hemolysis, Hb appears in 3 urine. The condition is called hemoglobinuria (hematuria). Structure of Hb Each molecule of Hb has two 1 pairs of polypeptide chains (globin) and 4 heme. Heme is a protoporphyrin IX 2 complexed with iron (Fe2+). Hb α2β2 tetramer 3 The heme carrier protein is molecule globin. binds four O2 The binding of O2 to Hb causes 4 oxidation of the divalent Fe to the Structure of Hb Heme has the unique ability to bind 5 or release oxygen. 6 1 g of Hb can bind 1.34 mL of O2.  Types of Hb tal and adult forms (HbF and HbA) In adult blood, HbA (98-99.9%) predominates. A little proportion of HbF occurs (0.1-2%). (The HbA subunits are α2β2). Infants have higher proportion of HbF (almost 80%). HbF is highest (98%) at birth, decreasing at 5% per week till 6 months when it wanes off. (The HbF subunits are α2γ2). Abnormal Hb Hemoglobinopathy is a type of genetic defect that results in abnormal structure of one of the globin chains Hemoglobinopathies Hb S (Hb Sickle Cell) r A single amino acid substitution (valine for glutamic acid) of the beta chain at the 6 position produces th an abnormal Hb – Hb S. The inheritance of two sickle cell Hb genes (Hb SS) r results in sickle cell anemia. On exposure to low oxygen concentration, the HbS r precipitates into elongated crystals, which distort the RBCs into a sickled (elongated) shape instead of a biconcave disc.  Sickle cell disease is characterized by occlusion r events in the vascular system that results in pain, organ failure and, occasionally, death. Hemoglobinopathies Hb Thalassemia This condition is due to diminished r production of one of the α-globin or β-globin chains of the Hb molecule. Equal numbers of Hb α- and β- chains are r necessary for normal function of Hb. However, imbalance in the Hb chain results in defect that destroys RBCs, thereby leading to There anemia. are α- and β- thalassemias – caused by r defects in the synthesis of α- and β- chains  Other abnormal forms of Hb Hb Stanleyville Hb Windsor Hb Johnstown Hb Hasharon Hb Randwick Hb Kenya Hb Ottawa Hb Matera Hb Hope Hb G-Ferrara Hb Footscray Hb Köln Hb St. Luke's Hb Howick Hb Stanmore Hb Maputo Hb Al-Hammadi Hb J-Guantanamo Hb Etobicoke Riyadh Hb Khartoum Hb S/O(Arab) Hb Manitoba Hb Osu- Hb G-Philadelphia Hb Hotel-Dieu Christiansborg Hb Matsue-Oki Hb Izmir Hb Lufkin Hb Dunn Hb Philly Hb Connecticut Hb Peterborough  Compounds formed by Hb Oxyhemoglo Carbhemoglobin Carboxyhemoglobin bin (HbCO2) (CO-Hb) (HbO2) HbO2 is formed HbCO2 is CO-Hb is when Hb formed from the formed combines with association O2. from the between Hb and association The normal CO2. between Hb arterial level of HbCO2 HbO2: 96-98%. and carbon The HbO2 maintains monoxide releases the O2 plasma (CO) Compounds formed by Hb Methemoglobin (MHb) MHb is formed via interaction HbO2 and HbCO2 of Hb with peroxides, organic are called nitro-containing compounds. The iron in MHb is oxidized to physiological Hb trivalent form. compounds Carboxyhemoglobin Excessive accumulation of and methemoglobin MHb in the blood posses a are pathological serious health risk to human compounds of Hb life (headache, coma, death). Normal Hb Level Hb level in males: 130-180 g / l (13-18 g/dl) Hb level in females: 120- 160g / l (12-16 g/dl). Other oxygen carrying proteins – members of the heme–globin family Myoglobin (O2 carrying protein expressed mainly in cardiac and striated muscles) Neuroglobin and Cytoglobin (intracellular O2 binding proteins in the brain)  Assignment With the aid of a well labeled diagram describe the hematopoietic pathways. Discuss hemoglobinization of RBCs. Thank You