Hematology-part-2.pdf

Slide 1 Slide 2 Platelets (Thrombocytes) Slide 3 Hemopoiesis (formation of blood cells) Platelets are formed in the bone marrow from megakaryocytes which are extremely large cells of the hematopoietic series in the marrow. Slide 4 Platelets Overview Slide 5 Platelets Characteristics...

Slide 1 Slide 2 Platelets (Thrombocytes) Slide 3 Hemopoiesis (formation of blood cells) Platelets are formed in the bone marrow from megakaryocytes which are extremely large cells of the hematopoietic series in the marrow. Slide 4 Platelets Overview Slide 5 Platelets Characteristics • The normal concentration of platelets in the blood is between 150,000 and 450,000/ μL. • Half-life in the blood of 8 to 12 days. • Eliminated from the circulation mainly by the tissue macrophage (Spleen). Slide 6 Platelets Cytoplasm • They do not have nuclei. • However they contain: 1. Contractile proteins: actin, myosin, and thrombosthenin. 2. Residuals of both the endoplasmic reticulum and the golgi apparatus. 3. Mitochondria (ATP). 4. Enzyme systems that synthesize prostaglandins. 5. Fibrin-stabilizing factor. 6. Vascular endothelial cells, vascular smooth muscle cells, and fibroblasts growth factors. Slide 7 Platelets membrane • There is a coat of glycoproteins that repulses adherence to normal endothelium and yet causes adherence to injured areas of the vessel wall. • Contains large amounts of phospholipids that activate multiple stages in the blood-clotting process. Slide 8 Platelets Thrombocytopenia • Petechiae • Cutaneous and mucosal bleeding Thrombocytopenia • Easily bruising • Increased bleeding time @MSD manual, pediatric UCI ** If the cut in the blood vessel is very small—many very small vascular holes develop throughout the body each day—the cut is often sealed by a platelet plug rather than by a blood clot. ** Literally thousands of small hemorrhagic areas develop each day under the skin (petechiae, which appear as purple or red dots on the skin) and throughout the internal tissues of a person who has few blood platelets. This phenomenon does not occur in persons with normal numbers of platelets. Slide 9 Hemostasis Slide 10 Hemostasis Blood vessel anatomy Slide 11 Hemostasis Events of hemostasis Hemostasis means prevention of blood loss and includes the following events: (1) Vascular constriction. (2) Formation of a platelet plug. (3) Formation of a blood clot as a result of blood coagulation. (4) Growth of fibrous tissue into the blood clot to close the hole in the vessel permanently. ** For bleeding to take place from a vessel, a break must be present in the vessel wall and the pressure inside must be greater than the pressure outside the vessel to force blood out through the defect. ** The small capillaries, arterioles, and venules are often ruptured by minor traumas of everyday life; such traumas are the most common source of bleeding, although we often are not even aware that any damage has taken place→ The body’s inherent hemostatic mechanisms normally are adequate to seal defects and stop blood loss through these small microcirculatory vessels. ** The rarer occurrence of bleeding from medium to large vessels usually cannot be stopped by hemostatic mechanisms alone. Bleeding from a severed artery is more profuse and therefore more dangerous than venous bleeding, because the outward driving pressure is greater in arteries (that is, arterial blood pressure is higher than venous pressure). ** First aid measures for a severed artery include applying external pressure to the wound that is greater than the arterial pressure to temporarily halt bleeding until the torn vessel can be surgically closed. Hemorrhage from a severed vein can often be stopped simply by elevating the bleeding body part to reduce gravity’s effects on pressure in the vein. If the accompanying drop in venous pressure is not enough to stop bleeding, mild external compression is usually adequate. Slide 12 Hemostasis 1. Vascular constriction • Immediately → smooth muscle contraction. • Reduces the flow of blood from the ruptured vessel. • The contraction results from the following: (1) local myogenic spasm (2) local autacoid factors from the traumatized tissues, vascular endothelium, and blood platelets. (3) nervous reflexes. • The spasm can last for many minutes or even hours, during which time the processes of platelet plugging and blood coagulation can take place. Slide 13 Hemostasis 2. Platelet plug formation ●Adhesion – The deposition of platelets on the subendothelial matrix ●Secretion – The release of platelet granule proteins (Form numerous irradiating pseudopods) (They secrete large quantities of ADP and thromboxane A2 → to activate nearby platelets.) ●Aggregation – Platelet-platelet cohesion Slide 14 Hemostasis 2. Platelet plug formation ** Platelets normally do not adhere to the smooth endothelial lining of blood vessels, but they do stick to damaged vessels. ** When the endothelial lining is disrupted because of vessel injury, von Willebrand factor (vWF), a plasma protein secreted by megakaryocytes, platelets, and endothelial cells and always present in the plasma, adheres to the exposed collagen. Thus vWF serves as a bridge between platelets and the injured vessel wall Slide 15 Hemostasis Control of platelet plug Slide 16 Hemostasis 2. Platelet plug formation The aggregated platelet plug not only physically seals the break in the vessel but also performs three other important roles: (1) The actin–myosin complex within the aggregated platelets contracts to compact and strengthen the plug. (2) The platelet plug releases several powerful vasoconstrictors that induce profound constriction. (3) The platelet plug releases other chemicals that enhance blood coagulation. Slide 17 Aspirin • Aspirin works by irreversibly inhibiting the enzyme cyclooxygenase (COX-1) which is required to make the precursors of thromboxane within platelets. • Thromboxane is required to facilitate platelet aggregation and to stimulate further platelet activation. Copyright 2009, John Wiley & Sons, Inc. Slide 18 Hemostasis Events of hemostasis Hemostasis means prevention of blood loss and includes the following events: (1) Vascular constriction. (2) Formation of a platelet plug. (3) Formation of a blood clot as a result of blood coagulation. (4) Fibrous organization or dissolution of the blood clot Slide 19 Hemostasis 3. Blood clot • Series of chemical reactions culminating in formation of fibrin threads. • Clotting (coagulation) factors – Ca2+, several inactive enzymes, various molecules associated with platelets or released by damaged tissues. ** The clot begins to develop in 15 to 20 seconds if the trauma to the vascular wall is severe and in 1 to 2 minutes if the trauma is minor. ** Within 3 to 6 minutes after rupture of a vessel, the entire opening or broken end of the vessel is filled with clot if the vessel opening is not too large. ** After 20 to 60 minutes, the clot retracts, which closes the vessel still further. Slide 20 Hemostasis 3. Blood clot • A meshwork of fibrin fibers running in all directions and entrapping blood cells, platelets, and plasma. • The fibrin fibers also adhere to damaged surfaces of blood vessels, thereby prevents further blood loss. Slide 21 Hemostasis 3. Clot retraction • Within a few minutes after a clot is formed, platelets begin to contract and usually express most of the fluid from the clot within 20 to 60 minutes. • As the clot retracts, the edges of the broken blood vessel are pulled together, thus contributing still further to hemostasis. • Serum: is blood plasma minus its fibrinogen and most of the other clotting factors. ** The platelets contribute directly to clot contraction by activating platelet thrombosthenin, actin, and myosin molecules. Slide 22 (a) Extrinsic pathway Hemostasis (b) Intrinsic pathway Tissue trauma Blood trauma Damaged endothelial cells expose collagen fibers Tissue factor (TF) 3. Blood coagulation Damaged platelets Activated XII 1. Extrinsic or intrinsic pathways lead to formation of prothrombinase. 2. Prothrombinase converts prothrombin into thrombin 3. Thrombin converts fibrinogen (soluble) into fibrin (insoluble) forming the threads of the clot Activated platelets Ca2+ Ca2+ + Platelet phospholipids Activated X Activated X V 1 Ca2+ Ca2+ V + PROTHROMBINASE (c) Common pathway Thrombin Ca 2+ Prothrombin (II) THROMBIN Ca2+ 2 XIII Fibrinogen (I) Activated XIII Loose fibrin threads STRENGTHENED FIBRIN THREADS 3 **In both the extrinsic and the intrinsic pathways, a series of different plasma proteins called blood-clotting factors plays a major role. **Most of these proteins are inactive forms of proteolytic enzymes. When converted to the active forms, their enzymatic actions cause the successive, cascading reactions of the clotting process **These factors are designated by roman numerals in the order in which the factors were discovered, not the order in which they participate in the clotting Process. **Prothrombin activator is generally considered to be formed in two ways, although, in reality, the two ways interact constantly with each other. Slide 23 Intrinsic Common pathway 1 prothrombinase Extrinsic 2 3 (Insoluble) ** Thus, the rate-limiting factor in causing blood coagulation is usually the formation of prothrombin activator and not the subsequent reactions beyond that point, because these terminal steps normally occur rapidly to form the clot. ** This cross-linkage is catalyzed by a clotting factor known as factor XIII (fibrin-stabilizing factor) Slide 24 Hemostasis Common pathway Slide 25 Hemostasis 3. Prothrombin and Thrombin • Prothrombin is a plasma protein (α2-globulin). • It is an unstable protein that can split easily into smaller compounds, one of which is thrombin (half MW). • Prothrombin is formed continually by the liver, and it is continually being used throughout the body for blood clotting. • Vitamin K is required by the liver for normal activation of prothrombin, as well as a few other clotting factors. • Much of the prothrombin first attaches to prothrombin receptors on the platelets already bound to the damaged tissue. Slide 26 Hemostasis 3. Action of Thrombin on Fibrinogen to Form Fibrin • Thrombin is an enzyme with weak proteolytic capabilities. • It acts on fibrinogen to remove four low-molecularweight peptides from each molecule of fibrinogen, forming one molecule of fibrin monomer. • Fibrin monomer has the automatic capability to polymerize with other fibrin monomer molecules to form fibrin fibers. Slide 27 Hemostasis 3. Action of Thrombin on Fibrinogen to Form Fibrin • In the early stages of polymerization, the fibrin monomer molecules are held together by weak noncovalent hydrogen bonding (weak clot). • Fibrin-stabilizing factor that is present in small amounts in normal plasma globulins but is also released from platelets entrapped in the clot (inactive). • Thrombin activates the fibrin-stabilizing factor which cause covalent bonds between more and more of the fibrin monomer molecules, as well as multiple cross-linkages between adjacent fibrin fibers, thus adding strength of the fibrin meshwork. Slide 28 Hemostasis Fibrinogen • Fibrinogen is a high-molecular-weight protein that occurs in the plasma. • Fibrinogen is formed in the liver. • Because of its large molecular size, little fibrinogen normally leaks from the blood vessels into the interstitial fluids, and because fibrinogen is one of the essential factors in the coagulation process, interstitial fluids ordinarily do not coagulate. **Yet, when the permeability of the capillaries becomes pathologically increased, fibrinogen does then leak into the tissue fluids in sufficient quantities to allow clotting of these fluids in much the same way that plasma and whole blood can clot. Slide 29 (a) Extrinsic pathway Hemostasis 3. Blood coagulation • Prothrombin activator is generally considered to be formed in two ways: (1) by the extrinsic pathway that begins with trauma to the vascular wall and surrounding tissues (2) by the intrinsic pathway that begins in the blood itself. (b) Intrinsic pathway Tissue trauma Blood trauma Damaged endothelial cells expose collagen fibers Tissue factor (TF) Damaged platelets Activated XII Activated platelets Ca2+ Ca2+ + Platelet phospholipids Activated X Activated X V 1 Ca2+ Ca2+ V + PROTHROMBINASE (c) Common pathway Ca2+ Prothrombin (II) THROMBIN Ca2+ 2 XIII Fibrinogen (I) Activated XIII Loose fibrin threads STRENGTHENED FIBRIN THREADS 3 *Extrinsic pathway Fewer steps then intrinsic and occurs rapidly Tissue factor (TF) leaks into the blood from cells outside (extrinsic to) blood vessels and initiates formation of prothrombinase *Intrinsic pathway More complex and slower than extrinsic Activators are either in direct contact with blood or contained within (intrinsic to) the blood Outside tissue damage not needed Also forms prothrombinase **The intrinsic and extrinsic mechanisms usually operate simultaneously. When a blood vessel ruptures during tissue injury, the intrinsic mechanism stops blood in the injured vessel, and the extrinsic mechanism clots blood that escaped into the tissue before the vessel was sealed off. Typically, clots are fully formed in 3 to 6 minutes. the extrinsic pathway can be explosive, limited only by the amount of tissue factor released from the traumatized tissues and by the quantities of Factors X, VII, and V in the blood. With severe tissue trauma, clotting can occur in as little as 15 seconds. The intrinsic pathway is much slower to proceed, usually requiring 1 to 6 minutes to cause clotting. ** Slide 30 Hemostasis 3. Extrinsic pathway 1. Release of tissue factor 2. Activation of factor X—role of factor VII and tissue factor. 3. Effect of Xa to form prothrombin activator—role of factor V TF ** Tissue factor: Traumatized tissue releases a complex of several factors called tissue factor. This factor is composed especially of phospholipids from the membranes of the tissue plus a lipoprotein complex that functions mainly as a proteolytic enzyme. ** 2. The activated Factor X combines immediately with tissue phospholipids that are part of tissue factors or with additional phospholipids released from platelets, as well as with Factor V to form the complex called prothrombin activator. ** 4. Thus, in the final prothrombin activator complex, activated factor X is the actual protease that causes splitting of prothrombin to form thrombin. Activated factor V greatly accelerates this protease activity, and platelet phospholipids act as a vehicle that further accelerates the process. Note especially the positive feedback effect of thrombin, acting through factor V, to accelerate the entire process once it begins. Slide 31 3. Intrinsic pathway 1. Blood trauma causes activation of factor XII and release of platelet phospholipids 2. Activation of factor XI 3. Activation of factor IX 4. Activation of factor X—role of factor VIII. ** (1) When factor XII is disturbed, such as by coming into contact with collagen or with a wettable surface such as glass, it takes on a new molecular configuration that converts it into a proteolytic enzyme called activated factor XII. Simultaneously, the blood trauma also damages the platelets because of adherence to collagen or to a wettable surface (or by damage in other ways); this releases platelet phospholipids that contain the lipoprotein called platelet factor 3, which also plays a role in subsequent clotting reactions. ** (4) The activated factor IX, acting in concert with activated factor VIII and the platelet phospholipids, activates factor X. Slide 32 Hemostasis hemophilia A or classic hemophilia (85%) : deficiency of Factor VIII hemophilia B (15%): deficiency of Factor IX. ** Hemophilia A and B are X-linked disorders that predominantly affect males. ** Patients with more severe hemophilia are more likely to have spontaneous bleeding. ** Immediate and delayed bleeding after trauma is common ** Common sites of bleeding in newborns include the central nervous system, and sites of medical interventions including circumcision, heel sticks, and venipunctures. ** Children – Bruising, joint bleeds, and other sites of musculoskeletal, and oral bleeding. Slide 33 (a) Extrinsic pathway Hemostasis 3. Blood coagulation (b) Intrinsic pathway Tissue trauma Blood trauma Damaged endothelial cells expose collagen fibers Tissue factor (TF) Thrombin has 2 positive feedback effects: • Accelerates formation of prothrombinase (V) • Thrombin activates platelets Damaged platelets Activated XII Activated platelets Ca2+ Ca2+ + Platelet phospholipids Activated X Activated X V 1 Ca2+ Ca2+ V + PROTHROMBINASE (c) Common pathway Ca2+ Prothrombin (II) THROMBIN Ca2+ 2 XIII Fibrinogen (I) Activated XIII Loose fibrin threads STRENGTHENED FIBRIN THREADS 3 *****Roles of Thrombin Multitasking thrombin, in addition to (1) converting fibrinogen into fibrin, (2) activates factor XIII to stabilize the resultant fibrin mesh (3) acts in a positive-feedback fashion to facilitate its own formation, (4) enhances platelet aggregation, which in turn is essential to the clotting process Slide 34 Think! Why do we use Ethylenediaminetetraacetic acid (EDTA) tube to collect blood for CBC? Except for the first two steps in the intrinsic pathway, calcium ions are required for promotion or acceleration of all the blood-clotting reactions. → Therefore, in the absence of calcium ions, blood clotting by either pathway does not occur. Slide 35 Slide 36 Hemostasis Events of hemostasis Hemostasis means prevention of blood loss and includes the following events: (1) Vascular constriction. (2) Formation of a platelet plug. (3) Formation of a blood clot as a result of blood coagulation. (4) Fibrous organization or dissolution of the blood clot Slide 37 Hemostasis 4. Fibrous organiazation The clot can become invaded by fibroblasts, which subsequently form connective tissue all through the clot (promoted at least partially by growth factor secreted by platelets) ** A clot is not meant to be a permanent solution to vessel injury. It is a transient device to stop bleeding until the vessel can be repaired. ** The aggregated platelets secrete a chemical that helps promote the invasion of fibroblasts from the surrounding connective tissue into the wounded area of the vessel. Fibroblasts form a scar at the vessel defect.. Slide 38 Hemostasis 4. Dissolution of clot **Plasminogen is a plasma protein, when activated, becomes a substance called plasmin (or fibrinolysin). When a clot is formed, a large amount of plasminogen is trapped in the clot along with other plasma proteins. The injured tissues and vascular endothelium very slowly release a powerful activator called tissue plasminogen activator few days later, after the clot has stopped the bleeding. t-PA eventually converts plasminogen to plasmin. which in turn removes the remaining unnecessary blood clot. **If clots were not removed after they performed their hemostatic function, their accumulation would eventually obstruct the vessels Slide 39 Prevention Normal Intravascular Anticoagulants ➢Endothelial surface factors ➢Antithrombin action of fibrin and antithrombin III. ➢Heparin. More than 50 important substances that cause or affect blood coagulation have been found in the blood and in the tissues—some that promote coagulation, called procoagulants, and others that inhibit coagulation, called anticoagulants. Whether blood will coagulate depends on the balance between these two groups of substances. In the blood stream, the anticoagulants normally predominate, so the blood does not coagulate while it is circulating in the blood vessels. However, when a vessel is ruptured, procoagulants from the area of tissue damage become activated and override the anticoagulants, and then a clot does develop. Slide 40 Prevention Endothelial Surface Factors • 1) the smoothness of the endothelial cell surface • 2) a layer of glycocalyx on the endothelium • 3) a protein bound with the endothelial membrane, thrombomodulin, which binds thrombin. • the thrombomodulin-thrombin complex also activates a plasma protein C, that acts as an anticoagulant by inactivating activated Factors V and VIII. • 4) Intact endothelial cells also produce other substances such a prostacyclin and nitric oxide (NO) that inhibit platelet aggregation and initiation of blood clotting **When the endothelial wall is damaged, its smoothness and its glycocalyx-thrombomodulin layer are lost, which activates both Factor XII and the platelets, thus setting off the intrinsic pathway of clotting. If Factor XII and platelets come in contact with the subendothelial collagen, the activation is even more powerful. Slide 41 Prevention Antithrombin Action of Fibrin and Antithrombin III. • Among the most important anticoagulants in the blood are those that remove thrombin from the blood. (1) the fibrin fibers that are formed during the process of clotting (85 to 90%) (2) The thrombin that does not adsorb to the fibrin fibers soon combines with antithrombin III. (an alphaglobulin) Slide 42 Prevention Heparin • Highly negatively charged conjugated polysaccharide • Powerful anticoagulant, but its concentration in the blood is normally low. • Widely used as a pharmacological agent. • Increases effectiveness of antithrombin III. • Inhibits thrombin, activated factors xII, xI, x, and Ix. • Produced in basophil and mast cells. Slide 43 Prevention Anticoagulants (Outside body ) • When blood is collected in a glass test tube normally clots in about 6 minutes. • Siliconized containers often does not clot for 1 hour or more. silicone prevents contact activation of platelets and Factor XII. • Heparin → when blood must be passed through a heart-lung machine or artificial kidney machine and then back into the person. • Soluble oxalate, citrate ion→ decreases the ionic calcium level → blood coagulation is blocked Slide 44 Thromboembolic Conditions Causes • A thrombus → an abnormal clot that develops in a blood vessel. • An embolus → freely flowing clots. • Emboli that originate in large arteries or in the left side of the heart → brain, kidneys, or elsewhere. • Emboli that originate in the venous system or in the right side of the → lungs (pulmonary embolism). Several factors, acting independently or simultaneously, can cause thromboembolism: (1) Roughened vessel surfaces associated with atherosclerosis can lead to thrombus formation (see p. 327). (2) Imbalances in the clotting–anticlotting systems can trigger clot formation. (3) Slow-moving blood is more apt to clot, probably because small quantities of fibrin accumulate in the stagnant blood, for example, in blood pooled in varicosed leg veins (see p. 364) or pooled in ineffectively pumping atria during atrial fibrillation (see p. 313). (4) Widespread clotting is occasionally triggered by release of tissue thromboplastin into the blood from large amounts of traumatized tissue. widespread clotting can occur in septicemic shock, in which bacteria or their toxins initiate the clotting cascade. Slide 45 Thromboembolic Conditions Causes • Cause of Thromboembolic Conditions (1) Any roughened endothelial surface of a vessel—as may be caused by arteriosclerosis, infection, or trauma—is likely to initiate the clotting process. (2) Blood often clots when it flows very slowly through blood vessels, where small quantities of thrombin and other procoagulants are always being formed. Slide 46 Thromboembolic Conditions DIC • Disseminated Intravascular Coagulation • This often results from the presence of large amounts of traumatized tissue in the body that releases great quantities of tissue factor into the blood. • Septicemia, in which either circulating bacteria or bacterial toxin • Plugging of small peripheral vessels greatly diminishes delivery of oxygen and other nutrients to the tissues. • Bleeding → The reason for this is that so many of the clotting factors are removed by the widespread clotting Slide 47 Think! There is genetically engineered tissue plasminogen activator (t-PA) available. When can you use tPA ? Slide 48 Self Reading! Prothrombin time [PT] Activated thromboplastin time [aptt]