Fibrinolysis: what is it? The process of fibrinolysis takes place in three phases Internal and external pathways of activation

In the process of formation of a hemostatic plug, mechanisms are activated aimed at limiting the growth of a thrombus, its dissolution and restoration of blood flow. All this is done by the fibrinolysis system. Fibrinolysis is the process of lysis of a thrombus or fibrin clot.

fibrinolysis system consists of enzymes, non-enzymatic protein cofactors and inhibitors fibrinolysis. The ultimate goal of this system is the formation of the fibrinolytic enzyme plasmin and the destruction of the fibrin clot. The system normally provides strictly local action, because its components are adsorbed on fibrin threads. The system includes 18 proteins and among them:

1. Plasminogen is a proenzyme from which the protein plasmin is formed, which breaks down fibrin. Activated by plasminogen activators (PA) and factor XIIa.

2. Tissue-type plasminogen activators (t-PA, tissue plasminogen activator) and urokinase ( u-PA, urokinase, urokinase plasminogen activator) are enzymes (serine proteases) that convert plasminogen to plasmin.

• tissue plasminogen activator (t-PA) is secreted by endothelium, monocytes, megakaryocytes,
• Urokinase plasminogen activator (u-PA) is produced by renal duct epithelial cells, juxtaglomerular cells, fibroblasts, macrophages, and endotheliocytes.

3. Factor XII (Hageman factor) - contact factor, plasminogen and prekallikrein activator.

4. Prekallikrein is a contact factor, Fletcher's factor, a proenzyme of kallikrein, catalyzing the formation of kinins, but for this it must first be activated by the Hageman factor (f. XIIa).

5. High molecular weight kininogen(HMC, Fitzgerald factor) - in the bloodstream is in combination with factor XII, is a prekallikrein receptor.

Converting plasminogen to plasmin

The key enzyme is plasmin, which hydrolyzes fibrin into soluble products. Transformation Activators plasminogen to plasmin are formed by the vascular wall ( internal activation) or tissues ( external activation).

Internal activation mechanism divided into Hageman-dependent (XIIa-dependent) and Hageman-independent (XIIa-independent):

• Hageman-dependent fibrinolysis occurs under the influence of factor XIIa, kallikrein and high molecular weight kininogen (HMK). This path is urgent character and is necessary for cleaning the vascular bed from unstabilized fibrin, which is formed in the process of intravascular blood coagulation.
• Hageman-independent fibrinolysis is carried out by kallikrein and VMK, but without the Hageman factor.

External activation pathway, dominant, is carried out with the participation of plasminogen activators t-PA and u-PA (urokinase).

The binding of plasminogen and its activators occurs on the fibrin clot. There is a lysine-binding site here, which is necessary for plasminogen activation by t-PA, which provides local formation of plasmin.

Regulation of plasmin synthesis from plasminogen

The breakdown of fibrin and fibrinogen

Plasmin is a very active and at the same time relatively non-specific serine protease that degrades fibrin and fibrinogen. The resulting molecules having different molecular weights are referred to as fibrin degradation products. They are mainly complexesDDE and D-dimers.

Some degradation products have a pronounced physiological activity - they reduce platelet aggregation and disrupt the polymerization of fibrin monomers, being, in essence, anticoagulants.

fibrinolysis reactions

fibrinolysis inhibitors

Plasminogen activator inhibitor type 1(RAI-1, plasminogen activator inhibitor-1) is the main inhibitor of fibrinolysis, synthesized by the vascular endothelium. Protein specifically inhibits the effect t-PA and u-RA, preventing their interaction with plasminogen. In turn, PAI-1 itself is inhibited protein C. Thus, protein C not only inhibits coagulation (through the inactivation of factors Va and VIIIa), but also enhances fibrinolysis.

α2-Antiplasmin is an enzyme (serine protease), a fast-acting plasmin inhibitor. It prevents plasminogen from being adsorbed on fibrin, reducing the amount of plasmin formed on the surface of the clot and thereby sharply slowing down fibrinolysis.

α2-Macroglobulin- inactivates thrombin, XIIa and plasmin. The mechanism of inhibition is the formation of the [α2-macroglobulin-protease] complex, which is then transferred to the liver.

Thrombin-activated fibrinolysis inhibitor (TAFI, thrombin-activated fibrinolysis inhibitor, carboxypeptidase Y), is activated by the thrombin-thrombomodulin complex. TAFI destroys catalytic surface fibrin (lysine-binding site) necessary for the action of t-PA. In addition, at higher concentrations, TAFI directly inhibits plasminogen, which prevents premature thrombus lysis.

More than 100 years ago, an interesting feature of blood was described - the ability of the formed clots to liquefy. Coagulation and fibrinolysis have recently been considered as independent processes. The clinical significance of fibrinolysis was associated mainly with the dissolution of an already pronounced thrombus. It was only after Astrup's research that it became known that the fibrinolytic process proceeds continuously throughout the entire vascular system and is necessary to maintain normal physiological functions.

As we have already said, blood coagulation and fibrinolysis are in a precisely balanced relationship with each other. Simultaneously with the latent process of deposition of a fibrin film on the intima of the arteries, this film is also dissolved as a result of the same latent fibrinolysis. Therefore, there is always some fibrinolytic activity in the blood. If it rises as a result of some pathological processes, hemorrhagic diathesis occurs; if it decreases, then this, according to Astrup, predisposes to sclerosis and its consequences.

In chronic cases, after a violation of microcirculation, deposits of cholesterol and lipids are most often formed. If this pathological picture reaches a noticeable development, they speak of atherosclerosis.

Fibrinolysis is also important for the release of secrets and hormones. It ensures the patency of the excretory ducts of various glands, such as the mammary, lacrimal or salivary, respiratory and urinary tracts, etc. Fibrin, formed during an inflammatory reaction, is necessary for the migration of histiocytes, and thus for the regeneration process. In such cases, it fulfills its role in a short time, after which it must be removed by fibrinolysis; the equilibrium then shifts towards lysis.

Arteriosclerotic changes in the vessels, up to the capillaries, can be prevented or at least reduced by increasing the endogenous fibrinolytic potential of the body by introducing proteases from outside.

If fibrinolysis is suppressed or below normal, there is an increased tendency to form scars after injuries, such as wound healing. In the case of inflammation of the serous membranes - such as the pleura or peritoneum - adhesions usually form, which can be prevented by increasing fibrinolysis.

The complications caused by the deposition of large amounts of fibrin after pleurisy, pericarditis or meningitis are also well known.

In contrast, the formation of abscesses in the lungs is caused by the opposite process - it can only be explained by the sudden onset of local fibrinolysis.

Local fibrinolysis also plays a role in the physiology of menstruation: it leads to the timely dissolution of blood clots that could interfere with blood flow.

From all that has been said, we see that plasmin and fibrin occupy a central place in fibrinolysis; Let us therefore proceed to a more detailed consideration of these substances.

fibrinolysis system- the antipode of the blood coagulation system. It ensures the dissolution of fibrin filaments, as a result of which normal blood flow is restored in the vessels.

It has a structure similar to the blood coagulation system:

1. components of the fibrinolysis system., located in the peripheral blood;
2. organs producing and utilizing components of the fibrinolysis system;
3. organs that destroy the components of the fibrinolysis system;
4. regulatory mechanisms.

The fibrinolysis system normally has a strictly local effect, since its components are adsorbed on fibrin filaments; under the action of fibrinolysis, the filaments dissolve, during hydrolysis, substances soluble in plasma are formed - fibrin degradation products (FDP) - they perform the function of secondary anticoagulants, and then are excreted from the body.

The value of the fibrinolysis system.

Dissolves fibrin threads, providing vascular recanalization.

Keeps the blood in a liquid state.

Components of the fibrinolysis system

Components of the fibrinolysis system:

1. plasmin (fibrinolysin);
2. fibrinolysis activators;
3. fibrinolysis inhibitors.

Plasmin- is produced in an inactive state in the form of plasminogen. By its nature, it is a protein of the globulin fraction, produced in the liver. A lot of it in the vascular wall. In granulocytes, endophiles, lungs, uterus, prostate and thyroid glands.

In its active state, plasmin is adsorbed on fibrin strands and acts as a proteolytic enzyme. In large quantities, plasmin can also mutate fibrinogen, forming degradation products of fibrin and fibrinogen (PDFF), which are also secondary anticoagulants.

With an increase in the amount of plasmin, the amount of fibrinogen decreases, hypo- or afibrinolytic bleeding occurs.

fibrinolysis activators- convert plasminogen to plasmin. They are divided into plasma and tissue.

Plasma activators include 3 groups of substances: various phosphatases of blood plasma - they are in an active state - these are active (direct) activators (physiological). In addition, trypsin: is produced in the pancreas, enters the duodenum, where it is absorbed into the blood. Normally, trypsin is found in the blood in the form of traces. When the pancreas is damaged, the concentration of trypsin in the blood increases sharply. It completely cleaves plasminogen, which leads to a sharp decrease in fibrinolytic activity.

Urokinase activity It is produced in the juxtaglomerular apparatus of the kidneys. Occurs in urine, so urine may have weak fibrinolytic activity.

Activators of bacterial origin- strepto- and staphyllokinases.

Indirect Activators- are in the plasma in an inactive state, lysokinase proteins are needed for their activation: tissue mucokinases - are activated during tissue injury; Plasma lysokinases are the most important coagulation factor XII.

tissue activators are found in tissues.

Their features:

1. are closely related to the cellular structure and are released only when the tissue is damaged;
2. are always active;
3. strong but limited effect.

Inhibitors are divided into:

1. inhibitors that prevent the conversion of plasminogen to plasmin;
2. preventing the action of active plasmin.

Now there are artificial inhibitors that are used to combat bleeding: E-aminocaproic acid, contrical, trasylol.

Phases of enzymatic fibrinolysis

Phases of enzymatic fibrinolysis:

I phase: activation of inactive activators. When a tissue is injured, tissue lysokinases are released, upon contact with damaged vessels, plasma lysokinases (plasma factor XII) are activated, i.e., activators are activated.

II phase: plasmiogen activation. Under the action of activators, the inhibitory group is cleaved off from plasminogen and it becomes active.

III phase: plasmin cleaves fibrin strands to PDF. If already active activators (direct) are involved, fibrinolysis proceeds in 2 phases.

The concept of enzymatic fibrinolysis

The process of non-enzymatic fibrinolysis proceeds without plasmin. The active principle is a complex of heparin C.

This process is controlled by the following substances.

1. thrombogenic proteins- fibrinogen, XIII plasma factor, thrombin;
2. macroergs- ADP of damaged platelets;
3. components of the fibrinolytic system: plasmin, plasminogen, activators and inhibitors of fibrinolysis;
4. hormones: adrenaline, insulin, thyroxine.

Essence: heparin complexes act on unstable fibrin filaments (fibrin S): after the action of a fibrin-stabilizing factor, heparin complexes (on fibrin J) do not act. With this type of fibrinolysis, there is no hydrolysis of fibrin filaments, but an informational change in the molecule (fibrin S passes from the fibrillar form to the tobular one).

The relationship of the blood coagulation system and the fibrinolysis system

Under normal conditions, the interaction of the blood coagulation system and the fibrinolysis system occurs in this way: microcoagulation is constantly taking place in the vessels, which is caused by the constant destruction of old platelets and the release of platelet factors from them into the blood. As a result, fibrin is formed, which stops when fibrin S is formed, which lines the walls of blood vessels with a thin film. Normalizing the movement of blood and improving its rheological properties.

The fibrinolysis system regulates the thickness of this film, which determines the permeability of the vascular wall. When the coagulation system is activated, the fibrinolysis system is also activated.

fibrinolysis(fibrin -f- Greek lysis dissolution, destruction) - the process of fibrin dissolution, carried out by the enzymatic fibrinelytic system. Fibrinolysis is a link in the body's anticoagulant system (see Blood coagulation system), which ensures the preservation of blood in the vascular bed in a liquid state.

During fibrinolysis, the fibrinolytic enzyme ilazmin, or fibriolysin (see), cleaves peptide bonds in the molecules of fibrin (see) and fibrinogen (see), as a result of which fibrin breaks down into plasma-soluble fragments, and fibrinogen loses its ability to coagulate. With fibrinolysis, the so-called. early fibrin and fibrinogen cleavage products are high-molecular fragments X and Y, and the X fragment retains the ability to coagulate under the influence of thrombin (see). Then fragments with a lower molecular weight (mass) are formed - the so-called. late cleavage products - fragments b and E. Fibrin and fibrinogen cleavage products have biological activity: early cleavage products have a pronounced antithrombin effect, late ones, especially fragment D, have anti-olimerase activity, the ability to inhibit platelet aggregation and adhesion (see), enhance the effect of kipi new (see).

The phenomenon of fibrinelysis was discovered in the 18th century, when the ability of blood to remain in a liquid state after sudden death was described. Currently, the process of fibrinolysis has been studied at the molecular level. The fibrinolytic system consists of four main components: plasmin proenzyme - plasminogen, active enzyme - plasmin, fiziol. plasminogen activators and inhibitors. Most of all plasminogen is contained in the blood plasma, from which it precipitates together with euglobulins or as part of fraction III during the precipitation of proteins according to the Kohn method (see Immunoglobulins). In the plasminogen molecule, under the action of activators, at least two peptide bonds are cleaved and active plasmin is formed. Plasmin is highly specific for the cleavage of lysyl-arginine and lysyl-lysine bonds in protein substrates, but fibrin and fibrinogen are specific substrates. Activation of ylazminogen into plasmin is carried out as a result of a proteolytic process caused by the action of a number of substances.

Physiological plasminogen activators are found in plasma and blood cells, in excretions (tears, breast milk, saliva, seminal fluid, urine), as well as in most tissues. By the nature of the action on the substrate, they are characterized as arginine esterases (see), splitting at least one arginylvaline bond in the plasminogen molecule. The following physiological plasminogen activators are known: plasma, vascular, tissue, renal or urokinase, coagulation factor XII (see Hemorrhagic diathesis), kallikrein (see Kinins). Besides, activation is carried out by trypsin (see), streptokinase, staphylokinase. Plasminogen activators, which are formed in the endothelium of blood vessels, play an important role in enhancing fibrinolysis. The formation of plasmin and fibrinolysis are carried out by the proenzyme and its activators immobilized (sorbed) on a fibrin clot. The activity of fibrinolysis is limited by the action of numerous inhibitors of plasmin and its activators. At least 7 inhibitors, or antiplasmins, are known to partially or completely inhibit plasmin activity. The main physiological fast-acting inhibitor is a2-antiplasmin, which is contained in the blood of healthy people at a concentration of 50-70 mg/l. It suppresses the fibrinolytic and esterase activity of plasmin almost instantly, forming a stable complex with the enzyme. The high affinity for plasmin determines the important role of this antiplasmin in the regulation of fibrinolysis in vivo. The second important inhibitor of plasmin is a2-macroglobulin with a molecular weight (mass) of 720 000-760 000. Its biological function is to protect the plasmin associated with it from self-digestion and the inactivating action of other iroteinases. a2-antiplasmin and a2-macroglobulin compete with each other when acting on plasmin. The ability to slowly inhibit the activity of plasmin has antithrombin III. In addition, o^-anti-trypsin, inter-a2-trypsin inhibitor, Cl-inactivator and o^-anti-chymotrypsin have an active effect. In the blood, placenta, amniotic fluid there are inhibitors of plasminogen activators: antiurokinase, antiactivators, antistreptokinase, inhibitor of plasminogen activation. The presence of a large number of fibrinolysis inhibitors is regarded as a form of protection of blood proteins from their cleavage by plasmin.

Since fibrinolysis is one of the links in the blood anticoagulant system, excitation of vascular chemoreceptors by the resulting thrombin leads to the release of plasminogen activators into the blood and rapid activation of the proenzyme. Normally, free plasmin is absent in the blood or it is associated with anti-plasmins. Activation of fibrinolysis occurs with emotional arousal, fright, fear, anxiety, trauma, hypoxia and hyperoxia, CO2 poisoning, physical inactivity, physical exertion and other influences leading to an increase in the permeability of the vascular wall. At the same time, high concentrations of plasmin appear in the blood, causing complete hydrolysis of fibrin, fibrinogen and other blood coagulation factors, which leads to impaired blood clotting. The cleavage products of fibrin and fibrinogen formed in the blood cause a violation of hemostasis (see). A feature of fibrinolysis is the ability to quickly activate.

To measure the fibrinolytic activity of blood, methods are used to determine plasmin activity, plasminogen activators and inhibitors - antiplasmins and antiactivators. Fibrinolytic activity of blood is determined by the time of lysis of blood clots, plasma or euglobulins isolated from plasma, by the concentration of fibrinogen lysed during incubation, or by the number of erythrocytes released from blood clots. In addition, the thromboplastic method is used (see Thromboelastography) and thrombin activity is determined (see). The content of plasminogen activators, plasmin and antiplasmins is determined by the size of the lysis zones (the product of two perpendicular diameters) formed on fibrin or fibrin-agar plates after applying plasma euglobulin solutions to them. The content of anti-activators is determined by simultaneously applying streptokinase or urokinase to the plates. The esterase activity of plasmin and activators is determined by the hydrolysis of chromogenic substrates or some arginine and lysine esters. Fibrinolytic activity of tissues is detected by the histochemical method by the size of the zones of lysis of fibrin plates after thin sections of an organ or tissue are applied to them.

Violation of fibrinolysis and the function of the fibrinolytic system leads to the development of pathological conditions. Inhibition of fibrinolysis contributes to thrombosis (see Thrombosis), the development of atherosclerosis (see), myocardial infarction (see), glomerulonephritis (see). The decrease in blood fibrinolytic activity is due to a decrease in the content of plasminogen activators in the blood due to a violation of their synthesis, the mechanism of release and depletion of reserves in cells, or an increase in the amount of antiplasmins and antiactivators. In an experiment on animals, a close relationship has been established between the content of blood coagulation factors (see Blood coagulation system), a decrease in fibrinolysis and the development of atherosclerosis. With reduced fibrinolysis, fibrin remains in the vascular bed, undergoes lipid infiltration and causes the development of atherosclerotic changes. In patients with atherosclerosis, fibrin and fibrinogen were found in lipid spots and atherosclerotic plaques. With glomerulonephritis, fibrin deposits were found in the renal glomeruli, which is associated with a sharp decrease in the fibrinolytic activity of the renal tissue and blood.

When fibrinolysis is inhibited, the drug fibrinolysin is administered intravenously (see) and plasminogen activators - streptokinase, urokinase, etc. (see Fibrinolytic agents), which increase the fibrinolytic activity of the blood, causing lysis of blood clots and their recanalization (see Thrombosis). This method of conservative treatment of thrombosis is theoretically substantiated as a method of simulating the protective reaction of the body's anticoagulant system against thrombosis. In the treatment of thrombosis and to prevent the formation of blood clots, fibrinolysis is increased by pharmacological non-enzymatic compounds administered orally; some of them have a fibrinolytic effect, inhibiting the activity of anti-plasmins, others indirectly cause the release of plasminogen activators from the vascular endothelium. Increase in the synthesis of fibrinolysis activators is promoted by anabolic steroids (see) with their long-term use and antidiabetic agents (see Hypoglycemic agents).

Excessive activation of fibrinolysis causes the development of hemorrhagic diathesis (see). The release of plasminogen activators into the blood, the formation of a large amount of plasmin contribute to the proteolytic cleavage of fibrinogen and blood coagulation factors, which leads to impaired hemostasis.

A number of researchers distinguish between primary and secondary increased fibrinolysis. Primary increased fibrinolysis is caused by massive penetration of plasminogen activators from tissues into the blood, which leads to the formation of plasmin, cleavage of V and VII blood coagulation factors, hydrolysis of fibrinogen, impaired platelet hemostasis and, as a result, to blood incoagulability, resulting in fibrinolytic bleeding (see .) - Primary general increased fibrinolysis can be observed with extensive injuries, cell breakdown under the influence of toxins, surgical interventions with extracorporeal circulation, with agony, acute leukemia, and also with chronic myeloid leukemia. Primary local increased fibrinolysis can cause hemorrhages during surgical interventions, in particular during prostatectomy, thyroidectomy, damage to organs with a high content of plasminogen activators, uterine bleeding (due to a sharply increased fibrinolytic activity of the endometrium). Primary local increased fibrinolysis can maintain and increase bleeding in peptic ulcer, damage to the oral mucosa, extraction of teeth, can be the cause of nosebleeds and fibrinolytic purpura.

Secondary increased fibrinolysis develops in response to disseminated intravascular coagulation (see Hemorrhagic diathesis, Thrombohemorrhagic syndrome, vol. 29, additional materials). This increases the bleeding that occurs due to the consumption of blood clotting factors. Differentiation of primary and secondary increased fibrinolysis is of practical importance. Primary increased fibrinolysis is characterized by a decrease in the content of fibrinogen, plasminogen, plasmin inhibitors and a normal content of platelets and prothrombin, therefore, the use of fibrinolysis inhibitors is indicated for it, which is contraindicated in secondary fibrinolysis.

For bleeding caused by increased fibrinolysis, synthetic inhibitors of fibrinolysis are prescribed - e-aminocaironic acid (see Aminocaproic acid), para-aminomethylbenzoic acid (amben), trasilol (see), etc. Treatment with fibrinolytic drugs and fibrinolysis inhibitors is monitored by determining the activity of thrombin by thromboelastographic and other methods characterizing the functional state of the blood coagulation and anticoagulation systems.

Bibliography: Andreenko G. V. Fibrinolysis. (Biochemistry, physiology, pathology), M., 1979; Biochemistry of animals and humans, ed. M. D. Kursky, v. 6, p. 84, 94, Kyiv, 1982; Kudryashov B. A. Biological problems of regulation of the liquid state of blood and its coagulation, M., 1975; Methods for the study of the fibrinolytic system of blood, ed. G. V. Andreenko, Moscow, 1981; Fibrinolysis, Modern fundamental and clinical concepts, ed. P. J. Gaffney and S. Balkuv-Ulyutina, trans. from English, M., 1982; H asov E. I. and L a-k and N K. M. Anticoagulants and fibrinolytic agents, M., 1977.

Physiology of fibrinolysis

fibrinolysis system- an enzymatic system that breaks down the fibrin strands that were formed during blood coagulation into soluble complexes. The fibrinolysis system is completely opposite to the blood coagulation system. Fibrinolysis limits the spread of blood coagulation through the vessels, regulates vascular permeability, restores their patency and ensures the liquid state of blood in the vascular bed. The fibrinolysis system includes the following components:

1) fibrinolysin (plasmin). It is found in an inactive form in the blood as profibrinolysin (plasminogen). It breaks down fibrin, fibrinogen, some plasma coagulation factors;

2) plasminogen activators (profibrinolysin). They belong to the globulin fraction of proteins. There are two groups of activators: direct action and indirect action. Direct-acting activators directly convert plasminogen into its active form, plasmin. Direct action activators - trypsin, urokinase, acid and alkaline phosphatase. Activators of indirect action are in the blood plasma in an inactive state in the form of a proactivator. For its activation, tissue and plasma lysokinase is required. Some bacteria have the properties of lysokinase. There are tissue activators in the tissues, especially a lot of them are found in the uterus, lungs, thyroid gland, prostate;

3) inhibitors of fibrinolysis (antiplasmins) - albumins. Antiplasmins inhibit the action of the enzyme fibrinolysin and the conversion of profibrinolysin to fibrinolysin.

During phase I, lysokinase, entering the bloodstream, brings the plasminogen proactivator into an active state. This reaction is carried out as a result of cleavage from the proactivator of a number of amino acids.

Phase II - the conversion of plasminogen into plasmin due to the cleavage of a lipid inhibitor under the action of an activator.

During phase III, under the influence of plasmin, fibrin is cleaved to polypeptides and amino acids. These enzymes are called fibrinogen / fibrin degradation products, they have a pronounced anticoagulant effect. They inhibit thrombin and inhibit the formation of prothrombinase, inhibit the process of fibrin polymerization, platelet adhesion and aggregation, enhance the effect of bradykinin, histamine, angiotensin on the vascular wall, which contributes to the release of fibrinolysis activators from the vascular endothelium.

Distinguish two types of fibrinolysis- enzymatic and non-enzymatic.

Enzymatic fibrinolysis carried out with the participation of the proteolytic enzyme plasmin. Fibrin is cleaved to degradation products.

Non-enzymatic fibrinolysis carried out by complex compounds of heparin with thrombogenic proteins, biogenic amines, hormones, conformational changes are made in the fibrin-S molecule.

The process of fibrinolysis goes through two mechanisms - external and internal.

Activation of fibrinolysis along the external pathway occurs due to tissue lysokinases, tissue plasminogen activators.

Proactivators and fibrinolysis activators are involved in the internal activation pathway, capable of converting proactivators into plasminogen activators or acting directly on the proenzyme and converting it into plasmin.

Leukocytes play a significant role in the process of fibrin clot dissolution due to their phagocytic activity. Leukocytes capture fibrin, lyse it and release its degradation products into the environment.

The process of fibrinolysis is considered in close connection with the process of blood coagulation. Their interconnections are carried out at the level of common pathways of activations in the reaction of the enzyme cascade, as well as due to neurohumoral mechanisms of regulation.