Immunohematology Lecture 2 PDF

HEMOSTASIS/ COAGULATION REGINA FRANCIS  CLASSIFICATION & STRUCTURE OF BLOOD VESSELS BLOOD VESSELS ARE THE CHANNELS OR CONDUITS THROUGH WHICH BLOOD IS DISTRIBUTED TO BODY TISSUES. THE VESSELS MAKE UP TWO CLOSED SYSTEMS OF TUBES THAT BEGIN AND END AT THE HEART. ONE SYSTEM...

HEMOSTASIS/ COAGULATION REGINA FRANCIS  CLASSIFICATION & STRUCTURE OF BLOOD VESSELS BLOOD VESSELS ARE THE CHANNELS OR CONDUITS THROUGH WHICH BLOOD IS DISTRIBUTED TO BODY TISSUES. THE VESSELS MAKE UP TWO CLOSED SYSTEMS OF TUBES THAT BEGIN AND END AT THE HEART. ONE SYSTEM, THE PULMONARY VESSELS, TRANSPORTS BLOOD FROM THE RIGHT VENTRICLE TO THE LUNGS AND BACK TO THE LEFT ATRIUM. THE OTHER SYSTEM, THE SYSTEMIC VESSELS, CARRIES BLOOD FROM THE LEFT VENTRICLE TO THE TISSUES IN ALL PARTS OF THE BODY AND THEN RETURNS THE BLOOD TO THE RIGHT ATRIUM. BASED ON THEIR STRUCTURE AND FUNCTION, BLOOD VESSELS ARE CLASSIFIED AS EITHER ARTERIES, CAPILLARIES, OR VEINS.  ARTERIES ARTERIES CARRY BLOOD AWAY FROM THE HEART. PULMONARY ARTERIES TRANSPORT BLOOD THAT HAS A LOW OXYGEN CONTENT FROM THE RIGHT VENTRICLE TO THE LUNGS. SYSTEMIC ARTERIES TRANSPORT OXYGENATED BLOOD FROM THE LEFT VENTRICLE TO THE BODY TISSUES  VEINS VEINS CARRY BLOOD TOWARD THE HEART. AFTER BLOOD PASSES THROUGH THE CAPILLARIES, IT ENTERS THE SMALLEST VEINS, CALLED VENULES. FROM THE VENULES, IT FLOWS INTO PROGRESSIVELY LARGER AND LARGER VEINS UNTIL IT REACHES THE HEART. IN THE PULMONARY CIRCUIT, THE PULMONARY VEINS TRANSPORT BLOOD FROM THE LUNGS TO THE LEFT ATRIUM OF THE HEART. THIS BLOOD HAS A HIGH OXYGEN CONTENT BECAUSE IT HAS JUST BEEN OXYGENATED IN THE LUNGS. SYSTEMIC VEINS TRANSPORT BLOOD FROM THE BODY TISSUE TO THE RIGHT ATRIUM OF THE HEART. THIS BLOOD HAS A REDUCED OXYGEN CONTENT BECAUSE THE OXYGEN HAS BEEN USED FOR METABOLIC ACTIVITIES IN THE TISSUE CELLS.  CAPILLARIES CAPILLARIES, THE SMALLEST AND MOST NUMEROUS OF THE BLOOD VESSELS, FORM THE CONNECTION BETWEEN THE VESSELS THAT CARRY BLOOD AWAY FROM THE HEART (ARTERIES) AND THE VESSELS THAT RETURN BLOOD TO THE HEART (VEINS). THE PRIMARY FUNCTION OF CAPILLARIES IS THE EXCHANGE OF MATERIALS BETWEEN THE BLOOD AND TISSUE CELLS.  ENDOTHELIAL CELL FUNCTION AND PLATELET ACTIVATION HEALTHY ENDOTHELIAL CELLS EXPRESS ANTIPLATELET AND ANTICOAGULANT AGENTS THAT PREVENT PLATELET AGGREGATION AND FIBRIN FORMATION, RESPECTIVELY. IN THE FACE OF ENDOTHELIAL DYSFUNCTION, ENDOTHELIAL CELLS TRIGGER FIBRIN FORMATION, AS WELL AS PLATELET ADHESION AND AGGREGATION. STRUCTURE OF PLATELETS  WHAT IS THE ROLE OF PLATELETS IN VASOCONSTRICTION? FOLLOWING VASOCONSTRICTION, EXPOSED COLLAGEN FROM THE DAMAGED SURFACE WILL ENCOURAGE PLATELETS TO ADHERE, ACTIVATE AND AGGREGATE TO FORM A PLATELET PLUG, SEALING OFF THE INJURED AREA.  MULTIPLE CHOICE QUESTIONS(MCQS) 1. WHAT DO YOU MEAN BY HEMOSTASIS? A. PRODUCTION OF NEW BLOOD CELLS B. PROCESS BY WHICH BLEEDING STOPS FROM DAMAGED BLOOD VESSELS C. NORMAL BODY CONDITION D. NONE OF THE ABOVE 2. WHICH OF THE FOLLOWING ARE THE 3 STEPS OF HEMOSTASIS? A. VASCULAR SPASM, PLATELET ADHESION, BLOOD CLOTTING B. VASCULAR SPASM, PLATELET PLUG FORMATION, BLOOD CLOTTING C. VASCULAR SPASM, PLATELET AGGREGATION, BLOOD CLOTTING D. VASCULAR SPASM, PLATELET RELEASE, BLOOD CLOTTING  3. WHY VASCULAR SPASM TAKES PLACE? A. DUE TO DAMAGE IN SMOOTH MUSCLE B. DUE TO RELEASE OF SUBSTANCES BY ACTIVATED PLATELETS C. DUE TO THE REFLEX INITIATED BY PAIN RECEPTORS D. ALL OF THE ABOVE 4. WHICH OF THE FOLLOWING OPTIONS DOES NOT COME UNDER THE SUBSTANCES RELEASED BY ACTIVATED PLATELETS? A. SEROTONIN B. ADP C. UREA D. CA IONS  5. WHICH SUBSTANCE ALONG WITH THROMBOXANE A2 HELPS ACTIVATE OTHER PLATELETS DURING PLATELET PLUG FORMATION? A. SEROTONIN B. ADP C. ATP D. LYSOSOMES 6. MATCH THE FOLLOWING- A) VASCULAR SPASM 1. EXTEND PROJECTION AND SUBSTANCES B)PLATELET ADHESION LIBERATE 2. CAUSES CONTRACTION IN WALLS OF BLOOD VESSEL C) PLATELET RELEASE ACTION 3. STICKING ON THE DAMAGED PART D) PLATELET ACCUMULATION 4. GATHERING OF ALL THE PLATELETS  SHORT ANSWER QUESTIONS 7. WHAT FACTORS ARE INVOLVED IN PRIMARY HEMOSTASIS? 8. WHAT TYPES OF DISEASES PRODUCE ABNORMALITIES IN PRIMARY HEMOSTASIS? 9. WHAT SIGNALS THE END OF PRIMARY HEMOSTASIS?  ANSWERS 1.PROCESS BY WHICH BLEEDING STOPS FROM DAMAGED BLOOD VESSEL 2.VASCULAR SPASM, PLATELET PLUG FORMATION, BLOOD CLOTTING 3.ALL OF THE ABOVE 4.UREA 5.ADP 6.A) – 2 B) – 3 C) – 1 D) – 4  ANSWERS 7. PRIMARY HEMOSTASIS IS THE FORMATION OF A WEAK PLATELET PLUG WHICH IS ACHIEVED IN FOUR PHASES: VASOCONSTRICTION, PLATELET ADHESION, PLATELET ACTIVATION, PLATELET AGGREGATION.  ANSWERS 8. DISORDERS OF PRIMARY HEMOSTASIS INHERITED: VON WILLEBRAND DISEASE. BERNARD-SOULIER SYNDROME. GLANZMANN THROMBASTHENIA. ACQUIRED. DRUG-INDUCED: E.G., ASPIRIN, NSAID, CLOPIDOGREL. IMMUNE THROMBOCYTOPENIC PURPURA. CHRONIC KIDNEY DISEASE. CARDIOPULMONARY BYPASS. 9. THE FORMATION OF THE PLATELET PLUG SIGNALS THE END OF PRIMARY HEMOSTASIS AND SERVES TO INITIATE UPCOMING PROCESSES ASSOCIATED WITH SECONDARY HEMOSTASIS.  LAORATORY TEST BLEEDING TIME – BLEEDING TIME IS A MEDICAL TEST DONE ON SOMEONE TO ASSESS THEIR PLATELET'S FUNCTION. IT INVOLVES MAKING A PATIENT BLEED, THEN TIMING HOW LONG IT TAKES FOR THEM TO STOP BLEEDING USING A STOPWATCH OR OTHER SUITABLE DEVICES. THE TERM TEMPLATE BLEEDING TIME IS USED WHEN THE TEST IS PERFORMED TO STANDARDIZED PARAMETERS. NORMAL RANGE GENERAL INTERPRETATIONS OF BLEEDING TIME ARE AS FOLLOWS: 1-9 MINUTES: NORMAL. 9- 15 MINUTES: PLATELET DYSFUNCTION. MORE THAN 15 MINUTES: CRITICAL; TEST MUST BE DISCONTINUED, AND PRESSURE SHOULD BE APPLIED. SECONDARY HEMOSTASIS  COAGULATION COAGULATION CAN BE DESCRIBED AS A MORE SOPHISTICATED PROCESS WITH THE FORMATION BLOOD CLOT. THE PROCESS IS SOMETIMES CHARACTERIZED AS A CASCADE, BECAUSE ONE EVENT PROMPTS THE NEXT AS IN A MULTI-LEVEL WATERFALL. THE RESULT IS THE PRODUCTION OF A GELATINOUS BUT ROBUST CLOT MADE UP OF A MESH OF FIBRIN—AN INSOLUBLE FILAMENTOUS PROTEIN DERIVED FROM FIBRINOGEN, THE PLASMA PROTEIN INTRODUCED EARLIER—IN WHICH PLATELETS AND BLOOD CELLS ARE TRAPPED.  AN INJURY TO A BLOOD VESSEL INITIATES THE PROCESS OF HEMOSTASIS. BLOOD CLOTTING INVOLVES FOUR STEPS. FIRST, VASCULAR SPASM CONSTRICTS THE FLOW OF BLOOD. NEXT, A PLATELET PLUG FORMS TO TEMPORARILY SEAL SMALL OPENINGS IN THE VESSEL. COAGULATION THEN ENABLES THE REPAIR OF THE VESSEL WALL ONCE THE LEAKAGE OF BLOOD HAS STOPPED. THE SYNTHESIS OF FIBRIN IN BLOOD CLOTS INVOLVES EITHER AN INTRINSIC PATHWAY OR AN EXTRINSIC PATHWAY, BOTH OF WHICH LEAD TO A COMMON PATHWAY.  CLOTTING FACTORS INVOLVED IN COAGULATION IN THE COAGULATION CASCADE, CHEMICALS CALLED CLOTTING FACTORS (OR COAGULATION FACTORS) PROMPT REACTIONS THAT ACTIVATE STILL MORE COAGULATION FACTORS. THE PROCESS IS COMPLEX, BUT IS INITIATED ALONG TWO BASIC PATHWAYS: THE EXTRINSIC PATHWAY, WHICH NORMALLY IS TRIGGERED BY TRAUMA. THE INTRINSIC PATHWAY, WHICH BEGINS IN THE BLOODSTREAM AND IS TRIGGERED BY INTERNAL DAMAGE TO THE WALL OF THE VESSEL.  BOTH OF THESE MERGE INTO A THIRD PATHWAY, REFERRED TO AS THE COMMON PATHWAY. ALL THREE PATHWAYS ARE DEPENDENT UPON THE 12 KNOWN CLOTTING FACTORS, INCLUDING CA2+ AND VITAMIN K. CLOTTING FACTORS ARE SECRETED PRIMARILY BY THE LIVER AND THE PLATELETS.  THE LIVER REQUIRES THE FAT-SOLUBLE VITAMIN K TO PRODUCE MANY OF THEM. VITAMIN K (ALONG WITH BIOTIN AND FOLATE) IS SOMEWHAT UNUSUAL AMONG VITAMINS IN THAT IT IS NOT ONLY CONSUMED IN THE DIET BUT IS ALSO SYNTHESIZED BY BACTERIA RESIDING IN THE LARGE INTESTINE. THE CALCIUM ION, CONSIDERED FACTOR IV, IS DERIVED FROM THE DIET AND FROM THE BREAKDOWN OF BONE. SOME RECENT EVIDENCE INDICATES THAT ACTIVATION OF VARIOUS CLOTTING FACTORS OCCURS ON SPECIFIC RECEPTOR SITES ON THE SURFACES OF PLATELETS.  EXTRINSIC PATHWAY THE QUICKER RESPONDING AND MORE DIRECT EXTRINSIC PATHWAY (ALSO KNOWN AS THE TISSUE FACTOR PATHWAY) BEGINS WHEN DAMAGE OCCURS TO THE SURROUNDING TISSUES, SUCH AS IN A TRAUMATIC INJURY. UPON CONTACT WITH BLOOD PLASMA, THE DAMAGED EXTRAVASCULAR CELLS, WHICH ARE EXTRINSIC TO THE BLOODSTREAM, RELEASE FACTOR III (THROMBOPLASTIN). SEQUENTIALLY, CA2+ THEN FACTOR VII (PROCONVERTIN), WHICH IS ACTIVATED BY FACTOR III, ARE ADDED, FORMING AN ENZYME COMPLEX. THIS ENZYME COMPLEX LEADS TO ACTIVATION OF FACTOR X (STUART–PROWER FACTOR), WHICH ACTIVATES THE COMMON PATHWAY DISCUSSED BELOW. THE EVENTS IN THE EXTRINSIC PATHWAY ARE COMPLETED IN A MATTER OF SECONDS.  INTRINSIC PATHWAY THE INTRINSIC PATHWAY (ALSO KNOWN AS THE CONTACT ACTIVATION PATHWAY) IS LONGER AND MORE COMPLEX. IN THIS CASE, THE FACTORS INVOLVED ARE INTRINSIC TO (PRESENT WITHIN) THE BLOODSTREAM. THE PATHWAY CAN BE PROMPTED BY DAMAGE TO THE TISSUES, RESULTING FROM INTERNAL FACTORS SUCH AS ARTERIAL DISEASE. HOWEVER, IT IS MOST OFTEN INITIATED WHEN FACTOR XII (HAGEMAN FACTOR) COMES INTO CONTACT WITH FOREIGN MATERIALS, SUCH AS WHEN A BLOOD SAMPLE IS PUT INTO A GLASS TEST TUBE.  INTRINSIC PATHWAY WITHIN THE BODY, FACTOR XII IS TYPICALLY ACTIVATED WHEN IT ENCOUNTERS NEGATIVELY CHARGED MOLECULES, SUCH AS INORGANIC POLYMERS AND PHOSPHATE PRODUCED EARLIER IN THE SERIES OF INTRINSIC PATHWAY REACTIONS. FACTOR XII SETS OFF A SERIES OF REACTIONS THAT IN TURN ACTIVATES FACTOR XI (ANTIHEMOLYTIC FACTOR C OR PLASMA THROMBOPLASTIN ANTECEDENT) THEN FACTOR IX (ANTIHEMOLYTIC FACTOR B OR PLASMA THROMBOPLASTIN). IN THE MEANTIME, CHEMICALS RELEASED BY THE PLATELETS INCREASE THE RATE OF THESE ACTIVATION REACTIONS. FINALLY, FACTOR VIII (ANTIHEMOLYTIC FACTOR A) FROM THE PLATELETS AND ENDOTHELIAL CELLS COMBINES WITH FACTOR IX (ANTIHEMOLYTIC FACTOR B OR PLASMA THROMBOPLASTIN) TO FORM AN ENZYME COMPLEX THAT ACTIVATES FACTOR X (STUART–PROWER FACTOR OR THROMBOKINASE), LEADING TO THE COMMON PATHWAY. THE EVENTS IN THE INTRINSIC PATHWAY ARE COMPLETED IN A FEW MINUTES.  COMMON PATHWAY BOTH THE INTRINSIC AND EXTRINSIC PATHWAYS LEAD TO THE COMMON PATHWAY, IN WHICH FIBRIN IS PRODUCED TO SEAL OFF THE VESSEL. ONCE FACTOR X HAS BEEN ACTIVATED BY EITHER THE INTRINSIC OR EXTRINSIC PATHWAY, THE ENZYME PROTHROMBINASE CONVERTS FACTOR II, THE INACTIVE ENZYME PROTHROMBIN, INTO THE ACTIVE ENZYME THROMBIN. (NOTE THAT IF THE ENZYME THROMBIN WERE NOT NORMALLY IN AN INACTIVE FORM, CLOTS WOULD FORM SPONTANEOUSLY, A CONDITION NOT CONSISTENT WITH LIFE.) THEN, THROMBIN CONVERTS FACTOR I, THE INSOLUBLE FIBRINOGEN, INTO THE SOLUBLE FIBRIN PROTEIN STRANDS. FACTOR XIII THEN STABILIZES THE FIBRIN CLOT.  FIBRINOLYSIS THE STABILIZED CLOT IS ACTED UPON BY CONTRACTILE PROTEINS WITHIN THE PLATELETS. AS THESE PROTEINS CONTRACT, THEY PULL ON THE FIBRIN THREADS, BRINGING THE EDGES OF THE CLOT MORE TIGHTLY TOGETHER, SOMEWHAT AS WE DO WHEN TIGHTENING LOOSE SHOELACES. THIS PROCESS ALSO WRINGS OUT OF THE CLOT A SMALL AMOUNT OF FLUID CALLED SERUM, WHICH IS BLOOD PLASMA WITHOUT ITS CLOTTING FACTORS.  FIBRINOLYSIS TO RESTORE NORMAL BLOOD FLOW AS THE VESSEL HEALS, THE CLOT MUST EVENTUALLY BE REMOVED. FIBRINOLYSIS IS THE GRADUAL DEGRADATION OF THE CLOT. AGAIN, THERE IS A FAIRLY COMPLICATED SERIES OF REACTIONS THAT INVOLVES FACTOR XII AND PROTEIN-CATABOLIZING ENZYMES. DURING THIS PROCESS, THE INACTIVE PROTEIN PLASMINOGEN IS CONVERTED INTO THE ACTIVE PLASMIN, WHICH GRADUALLY BREAKS DOWN THE FIBRIN OF THE CLOT. ADDITIONALLY, BRADYKININ, A VASODILATOR, IS RELEASED, REVERSING THE EFFECTS OF THE SEROTONIN AND PROSTAGLANDINS FROM THE PLATELETS. THIS ALLOWS THE SMOOTH MUSCLE IN THE WALLS OF THE VESSELS TO RELAX AND HELPS TO RESTORE THE CIRCULATION.  PLASMA ANTICOAGULANTS AN ANTICOAGULANT IS ANY SUBSTANCE THAT OPPOSES COAGULATION. SEVERAL CIRCULATING PLASMA ANTICOAGULANTS PLAY A ROLE IN LIMITING THE COAGULATION PROCESS TO THE REGION OF INJURY AND RESTORING A NORMAL, CLOT-FREE CONDITION OF BLOOD. FOR INSTANCE, A CLUSTER OF PROTEINS COLLECTIVELY REFERRED TO AS THE PROTEIN C SYSTEM INACTIVATES CLOTTING FACTORS INVOLVED IN THE INTRINSIC PATHWAY. TFPI (TISSUE FACTOR PATHWAY INHIBITOR) INHIBITS THE CONVERSION OF THE INACTIVE FACTOR VII TO THE ACTIVE FORM IN THE EXTRINSIC PATHWAY. ANTITHROMBIN INACTIVATES FACTOR X AND OPPOSES THE CONVERSION OF PROTHROMBIN (FACTOR II) TO THROMBIN IN THE COMMON PATHWAY. AND AS NOTED EARLIER, BASOPHILS RELEASE HEPARIN, A SHORT- ACTING ANTICOAGULANT THAT ALSO OPPOSES PROTHROMBIN. HEPARIN IS ALSO FOUND ON THE SURFACES OF CELLS LINING THE BLOOD VESSELS. A PHARMACEUTICAL FORM OF HEPARIN IS OFTEN ADMINISTERED THERAPEUTICALLY, FOR EXAMPLE, IN SURGICAL PATIENTS AT RISK FOR BLOOD CLOTS.  PLASMA ANTICOAGULANTS TFPI (TISSUE FACTOR PATHWAY INHIBITOR) INHIBITS THE CONVERSION OF THE INACTIVE FACTOR VII TO THE ACTIVE FORM IN THE EXTRINSIC PATHWAY. ANTITHROMBIN INACTIVATES FACTOR X AND OPPOSES THE CONVERSION OF PROTHROMBIN (FACTOR II) TO THROMBIN IN THE COMMON PATHWAY. AND AS NOTED EARLIER, BASOPHILS RELEASE HEPARIN, A SHORT-ACTING ANTICOAGULANT THAT ALSO OPPOSES PROTHROMBIN. HEPARIN IS ALSO FOUND ON THE SURFACES OF CELLS LINING THE BLOOD VESSELS. A PHARMACEUTICAL FORM OF HEPARIN IS OFTEN ADMINISTERED THERAPEUTICALLY, FOR EXAMPLE, IN SURGICAL PATIENTS AT RISK FOR BLOOD CLOTS.  LABS BLOOD SAMPLE ANTICOAGULATION THE MOST COMMNLY USED ANTICOAGULANT FOR COAGULATION SAMPLES IS TRISODIUM CITRATE. A 32 G/L (0.109 M) SOLUTION IS RECOMMENDED. FOR ROUTINE BLOOD COAGULATION TESTING, 9 VOLUMES OF LOOD IS ADDED TO 1 VOLUME OF ANTICOAGULANT. (4.5 ML SPECIMEN 0.5 ML OF ANTICOAGULANT.) WHEN THE HAEMATOCRIT IS ABNORMAL WITH EITHER SEVERE ANAEMIA OR POLYCYTHAEMIA THE BLOOD:CITRATE RATIO SHOULD BE ADJUSTED.  5 ML SPECIMEN HAEMATOCRIT CITRATE (ml) 0.20 0.70 0.25 0.65 0.30 0.61 0.55 0.39 0.60 0.36 0.65 0.31 0.70 0.27  HOMEWORK 1. WHY ARE OTHER ANTICOAGULANTS SUCH AS OXALATE, HEPARIN AND EDTA CONSIDERED UNSUITABLE FOR COAGULATION SAMPLES?