Lecture 3 Blood Blood • The only fluid tissue in the body • Composed of both cellular and liquid components • Considered a specialized liquid, connective tissue – contains fibrous proteins for clotting Composition of Blood • Plasma – non-living fluid matrix • Blood cells – Erythrocytes (red blood cells) – Leukocytes (white blood cells) – Platelets (cell fragments) Figure 17.1 The major components of whole blood. Slide 4 Formed elements 1 Withdraw blood and place in tube. © 2013 Pearson Education, Inc. 2 Centrifuge the blood sample. Plasma • 55% of whole blood • Least dense component Buffy coat • Leukocytes and platelets • <1% of whole blood Erythrocytes • 45% of whole blood (hematocrit) • Most dense component Interesting Facts about blood • Sticky, opaque fluid with metallic taste • Color varies with O2 content – High O2 - scarlet; Low O2 - dark red • pH 7.35–7.45 • ~8% of body weight • Average volume is 5–6 L for males; 4–5 L for females Function of Blood • Distribution – O2, metabolites, hormones, and metabolic waste • Regulation – pH of both blood and tissues – fluid volume • Protection – blood loss – infection Blood Plasma • 90% water • Over 100 dissolved solutes – Nutrients, gases, hormones, wastes, proteins, inorganic ions – Plasma proteins: • Remain in blood; not taken up by cells • Produced mostly by liver • 60% albumin; 36% globulins; 4% fibrinogen Blood Cells • WBCs are complete cells (heterogenous) • RBCs have no nuclei or organelles • Platelets are cell fragments • Survive in bloodstream only few days – originate in bone marrow and do not divide – terminally differentiated cells Figure 17.2 Photomicrograph of a human blood smear stained with Wright's stain. Platelets © 2013 Pearson Education, Inc. Neutrophils Erythrocytes Lymphocyte Monocyte Erythrocytes (RBCs) • Biconcave discs, anucleate • Filled with hemoglobin (Hb) (97%) for gas transport • Contain spectrin for structural support and flexibility • Major factor contributing to blood viscosity Figure 17.3 Structure of erythrocytes (red blood cells). 2.5 µm Side view (cut) 7.5 µm © 2013 Pearson Education, Inc. Top view Erythrocyte Function • Dedicated to respiratory gas transport via the protein hemoglobin • Hemoglobin binds reversibly with oxygen – binds irreversibly to carbon monoxide – less tightly binds CO2, most CO2 in plasma as bicarbonate (HCO3-) Figure 17.4 Structure of hemoglobin. Globin chains Heme group Globin chains Hemoglobin consists of globin (two alpha and two beta polypeptide chains) and four heme groups. © 2013 Pearson Education, Inc. Iron-containing heme pigment. Binding of Oxygen Contributes to Color of Blood • O2 loading in lungs – Produces oxyhemoglobin (ruby red) • O2 unloading in tissues – Produces deoxyhemoglobin or reduced hemoglobin (dark red) Oxygen Binding Affinity • Lower binding affinity – Higher levels of carbon dioxide – Lower pH (acidic) – Higher temperature Working muscle = hot, acidic, high CO2, needs oxygen. (Lungs) (Tissues) Formation of RBCs • Hematopoiesis • Blood cell formation in red bone marrow – In adult, found in axial skeleton, girdles, humerus and femur – 15 days to maturation, fully mature within 2 days of entering bloodstream Figure 17.5 Erythropoiesis: formation of red blood cells. Stem cell Committed cell Developmental pathway Phase 1 Ribosome synthesis Hematopoietic stem cell (hemocytoblast) Proerythroblast Basophilic erythroblast Phase 2 Hemoglobin accumulation Polychromatic erythroblast Phase 3 Ejection of nucleus Orthochromatic erythroblast Reticulocyte Erythrocyte Three stages: 1) Stem cell – Hematopoietic stem cell (hemocytoblast) 1) Committed cell – Proerythroblast 1) Developmental pathway – Basophilic erythroblasts develops into a mature erythrocyte Hematopoiesis • Committed Stage – Expression of protein receptors that respond to hormones and growth factors for maturation – Cell cannot revert back to a stem cell at this point • Requires Vitamin B12, folic acid, iron, and nutrients Regulation of Erythropoiesis • Too few erythrocytes leads to tissue hypoxia (oxygen deprivation) • Too many make the blood too viscous, poor circulation • Hormonal regulation Hormonal Control of Erythropoiesis • Erythropoietin (EPO) – a glycoprotein hormone • Stimulates Erythrocyte production from committed cells (proerythroblasts) • Kidney are major players in EPO production – triggered by low O2 levels (hypoxia) Figure 17.6 Erythropoietin mechanism for regulating erythropoiesis. Slide 1 Homeostasis: Normal blood oxygen levels 1 Stimulus: Hypoxia (inadequate O2 delivery) due to • Decreased RBC count • Decreased amount of hemoglobin • Decreased availability of O2 5 O2-carrying ability of blood rises. 4 Enhanced erythropoiesis increases RBC count. 3 Erythropoietin stimulates red bone marrow. © 2013 Pearson Education, Inc. 2 Kidney (and liver to a smaller extent) releases erythropoietin. Hormonal Regulation • Triggers for hypoxia – Loss of blood (hemorrhage or destruction) – Iron deficiencies leading to insufficient Hb in RBCs – Poor oxygen intake • Conversely, too many RBCs will inhibit erythropoietin production – Excessive oxygen Iron Requirements • Iron essential for hemoglobin synthesis – Iron from diet • Fe2+, Fe3+ are toxic to the body • Ferritin and Hemosiderin – protein-iron complex stored inside cells • Transferrine – transport protein for iron in blood Lifespan of RBCs • Between 100-120 days • Unable to synthesize new proteins • Engulfed by macrophage cells of spleen, liver and bone marrow – hemoglobin broken down into heme + globin – heme degraded to bilirubin and secreted Erythrocyte Disorders • Anemia – Blood has abnormally low O2-carrying capacity – Symtome rather than disease – Blood O2 levels cannot support normal metabolism – Accompanied by fatigue, pallor, shortness of breath, and chills Primary Causes of Anemia • Blood loss (hemorrhagic anemia) • Low RBC production – Iron deficiency – Autoimmune disease – Lack of EPO (hormonal imbalance) • High RBC destruction (hemolytic anemia) – Sickle cell anemia Figure 17.8 Sickle-cell anemia. Val His Leu Thr Pro Glu Glu … 1 2 3 4 5 6 7 146 Normal erythrocyte has normal hemoglobin amino acid sequence in the beta chain. Val His Leu Thr Pro Val Glu … 1 © 2013 Pearson Education, Inc. 2 3 4 5 6 7 146 Sickled erythrocyte results from a single amino acid change in the beta chain of hemoglobin. Erythrocyte Disorders • Polycythemia – Excessive number of erythrocytes • Polycythemia vera – a bone marrow cancer – Severely impair blood circulation • Secondary polycythemia – when less O2 available or hypersecretion of EPO Leukocytes (WBCs) • Make up <1% of total blood volume – 4,800 – 10,800 WBCs/μl blood • Function in defense against disease • Can leave blood stream via the capillaries (diapedesis) – Move through tissue spaces Figure 17.9 Types and relative percentages of leukocytes in normal blood. Formed elements (not drawn to scale) Differential WBC count (All total 4800– 10,800/ µl) Platelets Granulocytes Neutrophils (50–70%) Leukocytes Eosinophils (2–4%) Basophils (0.5–1%) Erythrocytes Agranulocytes Lymphocytes (25–45%) Monocytes (3–8%) © 2013 Pearson Education, Inc. Two Categories • Granulocytes – Visible cytoplasmic granules • Agranulocytes – No visible cytoplasmic granules • All of which play a role in the immune and inflammatory response (Ch. 21) Figure 17.10a Leukocytes. Granulocytes © 2013 Pearson Education, Inc. Neutrophil: Multilobed nucleus, pale red and blue cytoplasmic granules Figure 17.10b Leukocytes. Granulocytes © 2013 Pearson Education, Inc. Eosinophil: Bilobed nucleus, red cytoplasmic granules Figure 17.10c Leukocytes. Granulocytes © 2013 Pearson Education, Inc. Basophil: Bilobed nucleus, purplish-black cytoplasmic granules Figure 17.10d Leukocytes. Agranulocytes © 2013 Pearson Education, Inc. Lymphocyte (small): Large spherical nucleus, thin rim of pale blue cytoplasm Figure 17.10e Leukocytes. Agranulocytes © 2013 Pearson Education, Inc. Monocyte: Kidney-shaped nucleus, abundant pale blue cytoplasm Leukocyte Production • Leukopoiesis – the production of white blood cells (leukocytes) • Stimulated by chemical messengers – Interleukins (IL-1, IL-2, etc) – Colony-stimulating factors (CSFs) • named after cell population they stimulate (G-CSF) Figure 17.11 Leukocyte formation. Stem cells Hematopoietic stem cell (hemocytoblast) Lymphoid stem cell Myeloid stem cell Committed cells Myeloblast Developmental Promyelocyte pathway Eosinophilic myelocyte Myeloblast Myeloblast Monoblast Promyelocyte Promyelocyte Promonocyte Basophilic myelocyte Neutrophilic myelocyte Eosinophilic band cells Basophilic band cells Neutrophilic band cells (b) Basophils Neutrophils (c) Monocytes (d) B lymphocytes T lymphocytes (e) (f) Some become Some become Macrophages (tissues) Plasma cells © 2013 Pearson Education, Inc. T lymphocyte precursor Agranular leukocytes Granular leukocytes Eosinophils (a) B lymphocyte precursor Some become Effector T cells Granular Leukocytes • Mature granulocytes are stored in bone marrow • production is 3:1 ratio of granulocytes to erythrocytes • Much shorter lifespan due to function Agranular Leukocytes • Progression of agranulocytes differs • Monocytes – live several months • Lymphocytes – live few hours to decades – T lymphocyte precursors travel to thymus – B lymphocyte precursors remain in bone marrow Leukocyte Disorders • Leukopenia - abnormally low WBC count – drug induced (anti-inflammatory, anti cancer drugs) • Leukemias - Cancerous overproduction of abnormal WBCs – Named according to abnormal WBC clone involved Platelets • Cytoplasmic fragments of megakaryocytes • Contain granules that typically stain darker than outer region of the fragments – contain serotonin, Ca2+, enzymes, ADP, and platelet-derived growth factor (PDGF) for clotting • Development regulated by thrombopoietin – produced in liver and kidneys Figure 17.12 Formation of platelets. Stem cell Hematopoietic stem cell (hemocytoblast) Developmental pathway Megakaryoblast (stage I megakaryocyte) Megakaryocyte (stage II/III) Megakaryocyte (stage IV) Platelets Stage 1: Repeated mitoses but no cytokinesis Platelets formed by rupture as it presses against the capillaries in the red marrow © 2013 Pearson Education, Inc. Table 17.2 Summary of Formed Elements of the Blood (1 of 2) © 2013 Pearson Education, Inc. Table 17.2 Summary of Formed Elements of the Blood (2 of 2) © 2013 Pearson Education, Inc. Platelet Function • Form temporary platelet plug that helps seal breaks in blood vessels (clotting) • Process called hemostasis – fast, localized and controlled • Circulating platelets kept inactive and mobile by nitric oxide (NO) and prostacyclin from endothelial cells lining blood vessels Hemostasis • Fast series of reactions for stoppage of bleeding • Requires clotting factors, and substances released by platelets and injured tissues • Three steps – Vascular spasm – Platelet plug formation – Coagulation (blood clotting) Figure 17.13 Events of hemostasis. Step 1 Vascular spasm • Smooth muscle contracts, causing vasoconstriction. Collagen fibers Step 2 Platelet plug formation • Injury to lining of vessel exposes collagen fibers; platelets adhere. Platelets • Platelets release chemicals that make nearby platelets sticky; platelet plug forms. Fibrin © 2013 Pearson Education, Inc. Step 3 Coagulation • Fibrin forms a mesh that traps red blood cells and platelets, forming the clot. Slide 1 Mechanism of Vascular Spasm • Vasoconstriction of damaged blood vessel – helps in preventing blood loss • Triggers – Direct injury to vascular smooth muscle – Chemicals released by endothelial cells and platelets – Pain reflexes (pain receptors) Platelet Plug Formation • Positive feedback cycle • Damaged endothelium exposes collagen fibers – Normally release NO and prostacyclin (PGI2) • Platelets stick to collagen fibers via von Willebrand factor – plasma protein Collagen-Platelet Bridge • Stabilized by von Willebrand factor • Causes platelets to swell, become spiked and sticky, and release chemical messengers – ADP causes more platelets to stick and release their contents – Serotonin and thromboxane A2 enhance vascular spasm and platelet aggregation Coagulation • Reinforces platelet plug with fibrin threads – acts as a molecular glue • Blood transformed from liquid to gel • Series of reactions using clotting factors (procoagulants) – # I – XIII; many plasma proteins (Table 17.3) Figure 17.15 Scanning electron micrograph of erythrocytes trapped in a fibrin mesh. © 2013 Pearson Education, Inc. Three Clotting Phases 1. Extrinsic and Intrinsic pathways to Prothrombin Activation • Intrinsic – factors required are within blood • Extrinsic – factors required tissue factors outside blood, tissue factor (TF) • Platelet factor 3 (PF3) essential – phosphatidylserine on platelet membrane Ultimate Goal Phase 1 • Form prothrombin activator – Complex of Factor X, Ca2+, PF3 and Factor V • Prothrombin activator essential for phase 2 Figure 17.14 The intrinsic and extrinsic pathways of blood clotting (coagulation). (1 of 2) Phase 1 Intrinsic pathway Vessel endothelium ruptures, exposing underlying tissues (e.g., collagen) Extrinsic pathway Tissue cell trauma exposes blood to Platelets cling and their surfaces provide sites for mobilization of factors Tissue factor (TF) XII Ca2+ XIIa VII XI XIa VIIa Ca2+ IX IXa PF3 released by aggregated platelets VIII VIIIa TF/VIIa complex IXa/VIIIa complex X Xa Ca2+ PF3 © 2013 Pearson Education, Inc. Va Prothrombin activator V Phase 2: Common Pathway • Activation of thrombin via prothrombin activator • Prothrombin is cleaved to create and activate thrombin Phase 3: Common Pathway for Fibrin Mesh • Polymerization of Fibrin to create cross-linked mesh • Activated by the cleavage of Fibrinogen by Thrombin – thrombin stays bound to fibrin • Requires Ca2+ and Factor XIII Figure 17.14 The intrinsic and extrinsic pathways of blood clotting (coagulation). (2 of 2) Phase 2 Prothrombin (II) Thrombin (IIa) Phase 3 Fibrinogen (I) (soluble) Ca2+ Fibrin (insoluble polymer) XIII XIIIa Cross-linked fibrin mesh © 2013 Pearson Education, Inc. Blood clot, now what? • Clot retraction and fibrinolysis • Clot retraction stabilizes clot – Actin and myosin in platelets contract within 30– 60 minutes – Contraction pulls on fibrin strands, squeezing serum from clot – Draws ruptured blood vessel edges together Vessel Repair • Concurrent with clot retraction • Platelet-derived growth factor (PDGF) – stimulates division of smooth muscle cells and fibroblasts to rebuild blood vessel wall • Vascular endothelial growth factor (VEGF) – stimulates endothelial cells to multiply and restore endothelial lining Fibrinolysis • Critical to remove clots for proper blood flow • During clot formation, inactive plasminogen is inserted into clot • Plasminogen converted to plasmin by tissue plasminogen activator (tPA), factor XII and thrombin • Plasmin is a fibrin-digesting enzyme Regulating Clot formation • Two mechanisms limit clot size – Swift removal and dilution of clotting factors – Inhibition of activated clotting factors • Antithrombin III inactivates unbound thrombin, • Protein C inhibits clotting factors • Heparin activates antithrombin III Clotting is prevented in sites of no damage • Platelet adhesion is prevented by – Smooth endothelium of blood vessels prevents platelets from clinging – nitric oxide and prostacyclin secreted by endothelial cells • Vitamin E quinone acts as potent anticoagulant Disorders of Hemostasis • Thromboembolic disorders – undesirable clot formation – thrombus – clot in an unbroken vessel – emobolus – thrombus floating in bloodstream • Apirin, warfarin (coumadin) and heparin help counteract Disorders of Hemostasis • Bleeding disorders - abnormalities that prevent normal clot formation – Thrombocytopenia - deficient number of circulating platelets – Impaired Liver Function – synthesis of most clotting factors, – Hemophilia – Deficiencies in coagulating factors Human Blood Groups • RBC membranes bear 30 types of glycoprotein antigens • Anything perceived as foreign; generates an immune response – antigens promote agglutinization via antibody response • Mismatched transfused blood perceived as foreign Table 17.4 ABO Blood Groups © 2013 Pearson Education, Inc. Rh Factor • 52 named Rh agglutinogens (Rh factors) • C, D, and E are most common • Rh+ indicates presence of D antigen – Rh was initially identified in Rhesus monkeys, hence their name. • No anti-Rh antibodies in Rh- person – presence of Rh promotes an immune response against the foreign factor Rh Matching and Pregnancy • Erythroblastosis fetalis – Only occurs in Rh– mom with Rh+ fetus • Rh– mom exposed to Rh+ blood of fetus during delivery of first baby – baby healthy – Mother synthesizes anti-Rh antibodies • Second pregnancy – Mom's anti-Rh antibodies cross placenta and destroy RBCs of Rh+ baby Figure 17.16 Blood typing of ABO blood types. Serum Blood being tested Anti-B Anti-A Type AB (contains agglutinogens A and B; agglutinates with both sera) RBCs Type A (contains agglutinogen A; agglutinates with anti-A) Type B (contains agglutinogen B; agglutinates with anti-B) Type O (contains no agglutinogens; does not agglutinate with either serum) © 2013 Pearson Education, Inc. More bloodtyping • Other blood groups (MNS, Duffy, Kell, and Lewis) usually weak agglutinogens • Bombay (hh) blood group very rare – cannot receive blood from any ABO blood group Lab Exercise • First a quiz on Endrocrine system • Lab exercise 29 – We will not be using real blood! Sorry!