Plasmin is the leading enzyme of the fibrinolytic system, a biological process responsible for the dissolution of fibrin clots formed following vascular lesions. These intricate fibrin polymers are designed to create a sort of anti-hemorrhagic plug, which engulfs cells blood (platelets, white blood cells and red blood cells) and various plasma proteins, including the inactive precursor of plasmin, called plasminogen, which has a "high affinity for fibrin molecules. Thanks to this characteristic, plasminogen is concentrated above all in the sites where fibrin is deposited (such as clots).
The plasminogen is converted into plasmin thanks to the intervention of specific natural activators, among which we remember the urokinase (u-PA) and the tissue plasminogen activator (t-PA). Despite the name, the latter is more active at the level circulatory (it is generally secreted very slowly to allow the repair processes of the lesion), while urokinase is more active at the tissue level.Therefore, similarly to what has been seen for coagulation, in fibrinolysis we can distinguish an intrinsic and an extrinsic pathway, both consisting of a series of cascade reactions.
The fibrinolytic system limits the damage deriving from the excessive deposition of fibrin, and the consequent obstruction of the vessels, by abnormal clots (called thrombi).
With a proteolytic mechanism, the newly formed plasmin breaks down fibrin into soluble degradation products. The protease activity of plasmin is similar to that of pancreatic trypsin and is poorly specific (as well as on plasminogen it is also active on other substrates, such as the constituents of plasma complement, coagulation factors V and VIII, fibrinogen and some hormones of a natural proteins, such as ACTH, glucagon and growth hormone). From the proteolysis of fibrinogen and fibrin, peptide fragments of variable size originate, collectively called FDPs (degradation products of fibrinogen and fibrin).
As in the coagulation cascade, specific inhibitors also exist for the proteolytic cascade. In their absence, in fact, an "exaggerated demolition of fibrinogen, fibrin and other proteins important for coagulation would be produced, with the risk of serious bleeding.
During clot formation, plasmin synthesis is generally inhibited by specific substances released by activated platelets and local cells. Only in the presence of fibrin or stasis due to venous occlusion, the endothelium releases an excess quantity of plasminogen activators, which bind to specific receptors resulting in fibrinolysis. While in other body sites the plasmin receptors for the relative inhibitors ( the antiplasmins) are free, at the level of the clot they are engaged by the bond with fibrin; in this way the plasmin is protected from their action and is therefore free to fully carry out its activity.
Some drugs such as streptokinase enhance fibrinolytic activity and as such are useful in the phenomena of hypercoagulability of the blood (thrombosis). On the other hand, there are also antifibrinolytic drugs, particularly useful in patients with hyperfibrinolysis haemorrhages.
Select Blood Tests Blood Tests Uric acid - uricaemia ACTH: adrenocortitotropic hormone Alanine amino transferase, ALT, SGPT Albumin Alcoholism Alphafetoprotein Alphafetoprotein in pregnancy Aldolase Amylase Ammonemia, ammonia in the blood Androstenedione Antibody-endomysial antibodies Anti-gliadicides Nucleus Helicobacter pylori antibodies Embryo carcinoal antigen - CEA Prostate specific antigen PSA Antithrombin III Haptoglobin AST - GOT or aspartate aminotransferase Azotemia Bilirubin (physiology) Direct, indirect and total bilirubin CA 125: tumor antigen 125 CA 15-3: tumor antigen 19-9 as tumor marker Calcemia Ceruloplasmin Cystatin C CK-MB - Creatine kinase MB Cholesterolemia Cholinesterase (pseudcholinesterase) Plasma concentration Creatine kinase Creatinine Creatinine Creatinine clearance Chromogranin A D-dimer Hematocrit Blood culture Hemocrome Hemoglobin Glycated hemoglobin a Blood tests Blood tests, Down syndrome screening Ferritin Rheumatoid factor Fibrin and its degradation products Fibrinogen Leukocyte formula Alkaline phosphatase (ALP) Fructosamine and glycated hemoglobin GGT - Gamma-gt Gastrinemia GCT Glycemia Red blood cells Granulocytes HE4 and Cancer at "Ova" Immunoglobulins INR Insulinemia Lactate dehydrogenase LDH Leukocytes - white blood cells Lymphocytes Lipases Tissue damage markers MCH MCHC MCV Metanephrines MPO - Myeloperoxidase Myoglobin Monocytes MPV - average platelet volume Natremia Neutrophils Homocysteine Thyroid hormones OGTT Osmocyte Plasma protein A associated with pregnancy Peptide C Pepsin and pepsinogen PCT - platelet or platelet hematocrit PDW - distribution width of platelet volumes Platelets Plateletpenia PLT - number of platelets in blood Preparation for blood tests Prist Test Total IgEk Protein C (PC) - Protein C Activated (PCA) C Reactive Protein Rast Protein Test Specific IgE Reticulocytes Renin Reuma-Test Oxygen Saturation Sideremia BAC, BAC TBG - Thyroxine Binding Globulin Prothrombin Time Partial Thromblopastin Time (PTT) Activated Partial Thromboplastin Time (aPTT) Testosterone Testosterone: free and bioavailable fraction Thyroglobulin Thyroxine in the blood - Total T4, free T4 Transaminases High transaminases Transglutaminase Transferrin - TIBC - TIBC - UIBC - saturation of transferrin Transtyretin Triglyceridemia Triiodothyronine in the blood - Total T3, free T3 Troponin TRH and Troponins of s thymol to TRH TSH - Thyrotropin Uremia Liver values ESR VDRL and TPHA: serological tests for syphlis Volemia Conversion of bilirubin from mg / dL to µmol / L Conversion of cholesterol and triglyceridemia from mg / dL to mmol / L Conversion of creatinine from mg / dL to µmol / L Conversion of blood glucose from mg / dL to mmol / L Conversion of testosteronemia from ng / dL - nmol / L Conversion of uricemia from mg / dL to mmol / L
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