Thrombin Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Thrombin and links to relevant pages within the course.
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| Which of the following is not a likely cause of an abnormal thrombin time (TT): | View Page |
| This assay would be used to help rule out heparin contamination in a coagulation sample: | View Page |
| Factor V is primarily involved in: | View Page |
| Each of the following has been shown to induce platelet aggregation except: | View Page |
| Warfarin-based (coumarin derivative) oral anti-coagulant therapy is commonly monitored with : | View Page |
| Which changes Fibrinogen into Fibrin Monomer: | View Page |
| Which of the following statements about anticoagulant therapy is false? | View Page |
| Secondary Hemostasis – The Intrinsic Pathway Then, activated factor IX (IXa), along with ionized calcium, platelet factor, and factor VIII, activate factor X, which is a direct precursor of thrombin in the common pathway. The activation of factor X signals the beginning of the common pathway. The activated partial thromboplastin time (APTT) is used to monitor the intrinsic pathway and the effectiveness of heparin therapy. | View Page |
| Secondary Hemostasis – The Common Pathway The common pathway is sometimes referred to as the final common pathway or thrombin pathway. The common pathway starts with the activation of factor X by way of the intrinsic pathway, the extrinsic pathway, or both. Factor X is also referred to as either Stuart-Prower Factor or Thrombokinase. Factor X is manufactured in the liver, and is vitamin K dependant. | View Page |
| Secondary Hemostasis – The Common Pathway Activated factor X (Xa), in the presence of factor V (necessary cofactor), ionized calcium, and platelet factor act to convert prothrombin (precursor) to its active form, thrombin, by cleaving the prothrombin molecule. | View Page |
| Secondary Hemostasis – The Common Pathway Thrombin, after its conversion from prothrombin, catalyzes the conversion of fibrinogen into a fibrin monomer. Additionally, thrombin triggers the conversion of factor XIII into factor XIIIa which forms covalent bonds that crosslink and stabilize the fibrin monomers. Finally, thrombin feeds back into the intrinsic and common pathways, accelerating the action of factors XI, V, and VIII. | View Page |
| Fibrin/Fibrinogen Degradation Products and D-dimers The presence of D-dimers in plasma or whole blood indicates that fibrin has been formed and degraded (fibrinolysis). Plasmin can also degrade intact fibrinogen, generating fibrinogen degradation products that are detected in fibrin/fibrinogen degradation products (FDP) assays. D-dimers and FDP can become elevated whenever the coagulation and fibrinolytic systems are activated. The presence of D-dimer confirms that both thrombin and plasmin have been generated since it can only be produced as the result of the plasmin degradation of fibrin. This makes the test for D-dimers more specific for fibrinolysis than the FDP test that also detects the products of the direct proteolysis of fibrinogen (fibrinogenolysis).The D-dimer test can be useful in the diagnosis of deep venous thrombosis (DVT) or pulmonary embolism (PE), two forms of venous thromboembolism (VTE). When the test is being used for this purpose, it is important that D-dimer levels are accurately measured and accurately reported because of the serious nature of this clinical decision. If the test is positive in a patient suspected to have DVT or PE, clinicians proceed with further diagnostic tests. If the test is negative, depending on the clinical situation and the sensitivity of the D-dimer assay, DVT or PE is considered unlikely and further diagnostic tests for DVT or PE might not be pursued. D-dimer is a sensitive, but not specific, diagnostic test for disseminated intravascular coagulation, and an indicator of increased risk of future myocardial infarction in patients evaluated for chest pain. | View Page |
| Anticoagulation Therapy - Heparin Therapy The use of heparin is prophylactic. It is used either to prevent thromboembolism (a condition in which a blood clot forms inside a vessel), or used to limit a previous thromboembolism. Heparin inhibits thrombin. The degree of inhibition is dosage dependant. Low doses of heparin inhibit initial thrombin formation in the coagulation cascade, and act to slow down overall thrombin generation. At higher doses, heparin can inhibit thrombin entirely, making blood coagulation impossible. Heparin is a potent anticoagulant. Accurate monitoring is essential. The activated partial thromboplastin time (APTT) and/or activated clotting time is used to monitor unfractionated heparin therapy. | View Page |
| Anticoagulation Therapy - Oral Anticoagulant Therapy The therapeutic use of oral anticoagulants is typically the long-term solution for the patient in terms of managing situations of thrombosis. Warfarin, a dicumarol derivative, is one of the most popular oral anticoagulants used today. While heparin is administered intravenously and acts to inhibit thrombin, warfarin is given orally, taken in pill form, and functions as a Vitamin K antagonist. In earlier discussions, it was mentioned that certain clotting factors are considered to be vitamin K dependant. They require vitamin K molecules for their action to occur. Vitamin K dependant factors include factor II, VII, IX, and X. Vitamin K dependant metabolic processes involved with these coagulation factors are inhibited by drugs such as warfarin. The chemical structure of warfarin and similar anticoagulants enables them to bind competitively with free vitamin K. The prothrombin time (PT/INR) is used to monitor oral anticoagulant therapy. | View Page |
| Glossary of Terms A through M. Antibody - A modified type of serum globulin synthesized by lymphoid tissue in response to antigenic stimulus. By virtue of specific combining sites each antibody reacts with only one antigen. Anucleate - Having no nucleus. Azurophilic granules - The well-defined large reddish granules (lysosomes) which may be present in large lymphocytes. They are called "azurophilic granules" because they stain blue with the azure stains which were originally used. Basophilic granules - Specific granules present in the cytoplasm of basophils. These granules are large and stain purple-black due to their strong affinity for basic stain. B-cell - Bone marrow derived lymphocytes which produce humoral antibodies. Biconcave - Having two concave surfaces. Cellular Immunity - The capacity of a small proportion of lymphoid population to exhibit response to a specific antigen. Chromomere - The centrally located granular portion of the platelet. Clone - A population of cells descended from a single cell. Delayed Hypersensitivity - (part of cellular immunity) that develops slowly over a period of 24-72 hours after an antigenic stimulus. It consists of an accumulation of cells around small vessels and/or nerves. Example: Tuberculin skin test reaction. Digestive Enzyme - A substance that catalyzes or accelerates the process of digestion. Eosinophilic Granules - Specific granules present in the cytoplasm of eosinophils. These granules are large, refractile spheres which stain reddish-orange due to their strong affinity for acid stain. Erythrocyte (red blood cell, RBC) - One of the elements found in peripheral blood. Normally the mature form is a non-nucleated, circular, biconcave disk adapted to transport respiratory gases. Fixed Macrophage - A phagocyte that is non-motile. Free Macrophage - An ameboid phagocyte present at the site of inflammation. Graft Rejection - A transplanted tissue that is rejected by the body's antibodies. Graft vs. Host Reaction - A complication that occurs when an implanted piece of tissue, which contains antibodies, rejects the host's tissue. Granulocyte - A leukocyte which contains granules in its cytoplasm, i.e., neutrophilic, eosinophilic, or basophilic granules. Half-life - is the length of time it takes for half of the cells circulating at a given time to leave the blood for the tissues. Hemocyte - Any blood cell or formed element of the blood. Hemostasis - A mechanism of the vascular system to arrest an escape of blood. It involves an interaction between blood vessels, platelets, and coagulation. Heparin - A mucopolysaccharide acid which, when present in sufficient amounts, functions as an anticoagulant by inhibiting thrombin. Histamine - A powerful dilator of capillaries and a stimulator of gastric secretions. Humoral Immunity - Acquired immunity produced after response to an antigenic stimulus in which B cells produce circulating antibodies. Hyalomere - the clear, blue non-granular zone surrounding the chromomere of a platelet. Immune Response - The interaction of a cell and an antigen that results in a proliferation of the cell and a capacity to produce antibodies. Isotonic Fluid - A fluid whose elements have an equal osmotic pressure. Leukocyte (white blood cell, WBC) - One of the formed elements of the blood; involved primarily with the body's defense. Lysosome - A microscopic body within cell cytoplasm; contains various enzymes, mainly hydrolytic, which are released upon injury to the cell. Megakaryocyte - A giant cell of the bone marrow from which platelets are derived. Mononuclear - A cell having a single nucleus. | View Page |