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Blood moves in our body through blood vessels and is in a liquid state. But in the event of a violation of the integrity of the vessel, it forms a clot in a fairly short period of time, which is called a thrombus or “blood clot”. With the help of a blood clot, the wound is closed, thereby stopping the bleeding. The wound heals over time. Otherwise, if the blood clotting process is disrupted for some reason, a person may die from even minor damage.

Why does blood clot?

Blood clotting is very important defensive reaction human body. It prevents blood loss, while maintaining a constant volume of blood in the body. The coagulation mechanism is triggered by a change in the physicochemical state of the blood, which is based on the fibrinogen protein dissolved in its plasma.

Fibrinogen is able to turn into insoluble fibrin, which falls out in the form of thin threads. These same threads can form a dense network with small cells, which traps the formed elements. This is how a blood clot happens. Over time, the blood clot gradually thickens, tightens the edges of the wound and thereby promotes its speedy healing. When compacted, the clot releases a yellowish clear liquid, which is called whey.

Platelets also participate in blood clotting, which thicken the clot. This process is similar to making curd from milk, when casein (protein) is curdled and whey is also formed. During the healing process, the wound promotes gradual resorption and dissolution of the fibrin clot.

How does the coagulation process start?

A. A. Schmidt in 1861 found out that the process of blood clotting is completely enzymatic. He found that the conversion of fibrinogen, which is dissolved in plasma, into fibrin (an insoluble specific protein) occurs with the participation of thrombin, a special enzyme.

A person always has a little thrombin in his blood, which is in an inactive state, prothrombin, as it is also called. Prothrombin is formed in the human liver and is converted into active thrombin under the influence of thromboplastin and calcium salts present in the plasma. It must be said that thromboplastin is not found in the blood; it is formed only during the destruction of platelets and when other cells of the body are damaged.

The occurrence of thromboplastin is quite complex process, since in addition to platelets, some proteins contained in plasma are involved in it. In the absence of certain proteins in the blood, blood clotting may be slowed down or not occur at all. For example, if one of the globulins is missing in the plasma, then the well-known disease hemophilia (or, in other words, bleeding) develops. Those living with this condition can lose significant amounts of blood from even a small scratch.

Blood clotting phases

Thus, blood clotting is a step-by-step process that consists of three phases. The first is considered the most complex, during which the formation of the complex compound thromboplastin occurs. In the next phase, thromboplastin and prothrombin (an inactive plasma enzyme) are needed for blood clotting. The first has an effect on the second and thereby converts it into active thrombin. And in the final third phase, thrombin, in turn, affects fibrinogen (a protein that is dissolved in the blood plasma), turning it into fibrin, an insoluble protein. That is, with the help of coagulation, blood passes from a liquid to a jelly-like state.

Types of blood clots

There are 3 types of blood clots or thrombi:

1. A white thrombus is formed from fibrin and platelets; it contains a relatively small amount of red blood cells. Usually appears in those places of vessel damage where the blood flow is high (in the arteries).
2. Disseminated deposits of fibrin form in capillaries (very small vessels). This is the second type of blood clots.
3. And the last ones are red blood clots. They appear in places of slow blood flow and with the obligatory absence of changes in the vessel wall.

Clotting factors

The formation of a blood clot is a very complex process, involving numerous proteins and enzymes found in blood plasma, platelets and tissue. These are blood clotting factors. Those contained in plasma are usually designated by Roman numerals. Arabic indicates platelet factors. The human body contains all blood clotting factors that are in an inactive state. When a vessel is damaged, a rapid sequential activation of all of them occurs, as a result of which the blood clots.

Blood clotting, normal

In order to determine whether the blood clots normally, a test called a coagulogram is performed. It is necessary to do such an analysis if a person has thrombosis, autoimmune diseases, varicose veins veins, acute and chronic bleeding. It is also mandatory for pregnant women and those preparing for surgery. For this type of study, blood is usually taken from a finger or vein.

Blood clotting time is 3-4 minutes. After 5-6 minutes, it completely curls up and becomes a gelatinous clot. As for capillaries, a blood clot forms in about 2 minutes. It is known that with age, the time spent on blood clotting increases. So, in children from 8 to 11 years old, this process begins after 1.5-2 minutes, and ends after 2.5-5 minutes.

Blood clotting indicators

Prothrombin is a protein that is responsible for blood clotting and is an important component of thrombin. Its norm is 78-142%.

Prothrombin index (PTI) is calculated as the ratio of PTI, taken as a standard, to the PTI of the patient being examined, expressed as a percentage. The norm is 70-100%.

Prothrombin time is the period of time during which clotting occurs, normally 11-15 seconds in adults and 13-17 seconds in newborns. Using this indicator, you can diagnose DIC syndrome, hemophilia and monitor your blood condition when taking heparin. Thrombin time is the most important indicator; normally it ranges from 14 to 21 seconds.

Fibrinogen is a plasma protein that is responsible for the formation of a blood clot, and its amount can indicate inflammation in the body. In adults, its content should be 2.00-4.00 g/l, in newborns 1.25-3.00 g/l.

Antithrombin is a specific protein that ensures the resorption of the formed blood clot.

Two systems of our body

Of course, during bleeding, rapid blood clotting is very important to reduce blood loss to zero. It itself must always remain in a liquid state. But there are pathological conditions that lead to blood clotting inside the vessels, and this poses a greater danger to humans than bleeding. Diseases such as thrombosis of the coronary cardiac vessels, thrombosis pulmonary artery, thrombosis of cerebral vessels, etc., are associated with this problem.

It is known that two systems coexist in the human body. One promotes rapid blood clotting, while the second prevents this in every possible way. If both of these systems are in balance, then the blood will coagulate when the vessels are damaged externally, but inside them will be liquid.

What promotes blood clotting?

Scientists have proven that the nervous system can influence the educational process blood clot. Thus, blood clotting time decreases with painful stimulation. Conditioned reflexes may also influence coagulation. A substance such as adrenaline, which is released from the adrenal glands, promotes rapid blood clotting. At the same time, it is able to make the arteries and arterioles narrower and thus reduce possible blood loss. Vitamin K and calcium salts also participate in blood clotting. They help speed up this process, but there is another system in the body that interferes with it.

What prevents blood from clotting?

The cells of the liver and lungs contain heparin, a special substance that stops blood clotting. It prevents the formation of thromboplastin. It is known that the heparin content in young men and adolescents after work decreases by 35-46%, but in adults it does not change.

Blood serum contains a protein called fibrinolysin. It is involved in the dissolution of fibrin. It is known that moderate pain can accelerate clotting, however severe pain slows down this process. Low temperature prevents blood clotting. Body temperature is considered optimal healthy person. In the cold, blood clots slowly, sometimes this process does not occur at all.

Salts of acids (citric and oxalic), which precipitate calcium salts necessary for rapid coagulation, as well as hirudin, fibrinolysin, sodium citrate and potassium, can increase the clotting time. Medical leeches can produce with the help of the cervical glands a special substance - hirudin, which has an anti-clotting effect.

Clotting in newborns

In the first week of a newborn’s life, blood clotting occurs very slowly, but already during the second week, the levels of prothrombin and all coagulation factors approach the adult norm (30-60%). Already 2 weeks after birth, the fibrinogen content in the blood increases greatly and becomes like that of an adult. By the end of the first year of life, the content of other blood clotting factors approaches the adult norm. They reach the norm by 12 years.

Blood clotting must be normal, so hemostasis is based on equilibrium processes. It is impossible for our valuable biological fluid collapsed - this threatens with serious, deadly complications (). On the contrary, the slow formation of a blood clot can result in uncontrolled massive bleeding, which can also lead to the death of a person.

The most complex mechanisms and reactions, involving a number of substances at one stage or another, maintain this balance and thus enable the body to cope quite quickly on its own (without the involvement of any outside help) and recover.

The rate of blood clotting cannot be determined by any one parameter, because many components that activate each other are involved in this process. In this regard, tests for blood clotting are different, where their intervals normal values mainly depend on the method of conducting the research, and also in other cases - on the gender of the person and the days, months, and years he has lived. And the reader is unlikely to be satisfied with the answer: “ Blood clotting time is 5 - 10 minutes". A lot of questions remain...

Everyone is important and everyone is needed

Stopping bleeding relies on an extremely complex mechanism, including many biochemical reactions, in which a huge number of different components are involved, where each of them plays its own specific role.

blood clotting diagram

Meanwhile, the absence or failure of at least one coagulation or anticoagulation factor can disrupt the entire process. Here are just a few examples:

• An inadequate reaction from the walls of blood vessels disrupts the blood platelets - which “feels” primary hemostasis;
• The low ability of the endothelium to synthesize and secrete inhibitors of platelet aggregation (the main one is prostacyclin) and natural anticoagulants () thickens the blood moving through the vessels, which leads to the formation of absolutely unnecessary for the body packages, which for the time being can calmly “sit” attached to the wall of a vessel. These become very dangerous when they break off and begin to circulate in the bloodstream - thereby creating a risk of vascular accident;
• The absence of a plasma factor such as FVIII causes a sex-linked disease - A;
• Hemophilia B is detected in a person if, for the same reasons (a recessive mutation in the X chromosome, which, as is known, there is only one in men), Christman factor deficiency (FIX) occurs.

In general, everything begins at the level of the damaged vascular wall, which, secreting substances necessary to ensure blood clotting, attracts blood platelets circulating in the bloodstream - platelets. For example, one that “calls” platelets to the site of an accident and promotes their adhesion to collagen, a powerful stimulator of hemostasis, must begin its activity in a timely manner and work well so that in the future one can count on the formation of a full-fledged plug.

If platelets use their functional capabilities (adhesive-aggregation function) at the proper level, other components of primary (vascular-platelet) hemostasis quickly come into play and short terms form a platelet plug, then in order to stop the blood flowing from the microcirculatory vessel, it is possible to do without the special influence of other participants in the blood coagulation process. However, the body cannot cope without plasma factors to form a full-fledged plug capable of closing an injured vessel that has a wider lumen.

Thus, at the first stage (immediately after injury to the vascular wall), successive reactions begin to occur, where the activation of one factor gives impetus to bringing the others into an active state. And if something is missing somewhere or a factor turns out to be untenable, the process of blood clotting is slowed down or stops altogether.

In general, the coagulation mechanism consists of 3 phases, which must ensure:

• The formation of a complex complex of activated factors (prothrombinase) and the conversion of protein synthesized by the liver - into thrombin ( activation phase);
• Transformation of protein dissolved in the blood - factor I (, FI) into insoluble fibrin is carried out in coagulation phase;
• Completion of the coagulation process with the formation of a dense fibrin clot ( retraction phase).

Blood clotting tests

Multi-stage cascade enzymatic process, ultimate goal which is the formation of a clot capable of closing the “gap” in the vessel, the reader will probably seem confusing and incomprehensible, so a reminder will suffice that this mechanism provide various factors coagulation, enzymes, Ca 2+ (calcium ions) and a variety of other components. However, in this regard, patients are often interested in the question: how to detect if something is wrong with hemostasis or to calm down knowing that the systems are working normally? Of course, there are blood clotting tests for such purposes.

The most common specific (local) analysis of the state of hemostasis is considered to be widely known, often prescribed by therapists, cardiologists, as well as obstetricians-gynecologists, and the most informative.

Meanwhile, it should be noted that conducting such a number of tests is not always justified. It depends on many circumstances: what the doctor is looking for, at what stage of the reaction cascade he focuses his attention, how much time is available medical workers etc.

Simulation of the extrinsic blood clotting pathway

For example, the extrinsic pathway for activating coagulation in laboratory conditions can simulate a test called by doctors Quick's prothrombin, Quick's test, prothrombin (PTT) or thromboplastin time (all these are different designations for the same test). The basis of this test, which depends on factors II, V, VII, X, is the participation of tissue thromboplastin (it is added to citrate recalcified plasma during work on a blood sample).

The limits of normal values ​​in men and women of the same age do not differ and are limited to the range of 78 – 142%, however, in women expecting a child, this figure is slightly increased (but slightly!). In children, on the contrary, the norms are within lower values ​​and increase as they approach adulthood and beyond:

Reflection of the internal mechanism in a laboratory setting

Meanwhile, to determine a blood clotting disorder caused by a malfunction of the internal mechanism, tissue thromboplastin is not used during the analysis - this allows the plasma to use exclusively its own reserves. In a laboratory setting, the internal mechanism is traced by waiting for blood taken from the vessels of the bloodstream to clot on its own. The onset of this complex cascade reaction coincides with the activation of the Hageman factor (factor XII). The launch of this activation is ensured by various conditions(contact of blood with damaged vessel wall, cell membranes, which have undergone certain changes), which is why it is called contact.

Contact activation also occurs outside the body, for example, when blood enters a foreign environment and comes into contact with it (contact with glass in a test tube, instruments). The removal of calcium ions from the blood does not in any way affect the launch of this mechanism, however, the process cannot end with the formation of a clot - it breaks off at the stage of activation of factor IX, where without ionized calcium no longer possible.

The clotting time of blood, or the time during which it, having previously been in a liquid state, is poured into the form of an elastic clot, depends on the rate of conversion of the fibrinogen protein dissolved in plasma into insoluble fibrin. It (fibrin) forms threads that hold red blood cells (erythrocytes), causing them to form a bundle that closes the hole in the damaged blood vessel. Blood clotting time (1 ml taken from a vein - Lee-White method) in such cases is limited on average to 4 - 6 minutes. However, the blood clotting rate certainly has a wider range of digital (time) values:

1. Blood taken from a vein takes 5 to 10 minutes to form a clot;
2. The Lee-White clotting time in a glass test tube is 5–7 minutes, in a silicone test tube it extends to 12–25 minutes;
3. For blood taken from a finger, the following indicators are considered normal: the beginning is 30 seconds, the end of bleeding is 2 minutes.

An analysis reflecting the internal mechanism is applied at the first suspicion of gross violations blood clotting. The test is very convenient: it is carried out quickly (while the blood is flowing or a clot is forming in a test tube), it does not require special reagents or complex equipment, special training the patient does not need it. Of course, blood clotting disorders discovered in this way give reason to assume a number of significant changes in the systems that provide normal condition hemostasis, and force further research to identify true reasons pathology.

With an increase (lengthening) of blood clotting time, you can suspect:

• Deficiency of plasma factors intended to ensure coagulation, or their congenital inferiority, despite the fact that they are at a sufficient level in the blood;
• Serious liver pathology resulting in functional failure of the organ parenchyma;
• (in the phase when the ability of blood to clot decreases);

Blood clotting time lengthens when heparin therapy is used, so patients receiving this drug have to undergo tests indicating the state of hemostasis quite often.

The considered indicator of blood clotting decreases its values ​​(shortens):

• In the high coagulation phase () of DIC syndrome;
• For other diseases causing pathological condition hemostasis, that is, when the patient already has bleeding disorders and is classified in the group increased risk blood clot formation (thrombosis, etc.);
• In women using for contraception or for long-term treatment purposes oral agents containing hormones;
• In women and men taking corticosteroids (when corticosteroid drugs are prescribed, age is very important– many of them can cause significant changes in hemostasis in children and the elderly, and are therefore prohibited for use in this group).

In general, the norms differ little

Indicators of blood clotting (normal) in women, men and children (meaning one age for each category), in principle, differ little, although certain indicators in women change physiologically (before, during and after menstruation, during pregnancy), therefore, the gender of an adult is still taken into account when conducting laboratory research. In addition, for women during the period of bearing a child, certain parameters even have to shift somewhat, because the body has to stop bleeding after childbirth, so the coagulation system begins to prepare in advance. An exception in relation to some indicators of blood clotting is the category of children in the first days of life, for example, in newborns the PTT is a couple of times higher than in adult males and females (the norm for adults is 11 - 15 seconds), and in premature infants the prothrombin time increases for 3 – 5 seconds. True, by about the 4th day of life, PTT decreases and corresponds to the normal blood clotting of adults.

The table below will help the reader to get acquainted with the norms of individual indicators of blood clotting, and, possibly, compare them with their own parameters (if the test was carried out relatively recently and there is a form recording the results of the study on hand):

Laboratory test	Normal blood clotting index values	Material used
Platelets: In women In men In children	180 – 320 x 10 9 /l 200 – 400 x 10 9 /l 150 – 350 x 10 9 /l	Capillary blood(from a finger)
Clotting time: According to Sukharev According to Lee-White	Start – 30 - 120 seconds, end – 3 - 5 minutes 5 - 10 minutes	Capillary Blood taken from a vein
Duration of bleeding according to Duke	no more than 4 minutes	blood from finger
Thrombin time(indicator of fibrinogen conversion to fibrin)	12 – 20 seconds	venous
PTI (prothrombin index): Blood from a finger Blood from a vein	90 – 105%	Capillary Venous
APTT (activated partial thromboplastin time, kaolin-kephalin time)	35 - 50 seconds (does not correlate with gender and age)	blood from a vein
Fibinogen: In adult men and women In women in the last month of the third trimester of pregnancy In children of the first days of life	2.0 – 4.0 g/l 1.25 – 3.0 g/l	Venous blood

In conclusion, I would like to draw the attention of our regular (and new, of course) readers: perhaps reading the review article will not fully satisfy the interest of patients affected by hemostatic pathology. People who first encountered similar problem, as a rule, want to get as much information as possible about the systems that provide bleeding control in right moment, and preventing the formation dangerous clots, so they start looking for information on the Internet. Well, you shouldn’t rush - in other sections of our website a detailed (and, most importantly, correct) description of each of the indicators of the state of hemostasis is given, the range of normal values ​​is indicated, and indications and preparation for analysis are also described.

Video: simply about blood clotting

Video: report on blood clotting tests

One of the presenters will answer your question.

IN at the moment Answers questions: A. Olesya Valerievna, candidate of medical sciences, teacher at a medical university

Blood clotting. The cells of a multicellular organism live and are in contact with their own fluid environment. This environment consists of blood plasma, tissue fluid and lymph and is called the internal fluid of the body. In composition it differs from external environment, surrounding whole organism. Therefore, there is a vital need in cases of violation of its integrity to preserve this liquid internal environment within its natural course. In higher vertebrates and humans, a blood coagulation system arose in the process of evolution. Moreover, the value of the coagulation system is higher organisms much broader than the concept of hemostasis or stopping bleeding when the integrity of the vascular wall is violated.

Blood clotting is a protective reaction of the body. The blood released from the vessel coagulates within 3-4 minutes, i.e. it passes from a liquid state to a jelly-like state. Blood clotting occurs when the soluble plasma protein fibrinogen is converted into insoluble fibrin.

Blood clotting occurs in several stages. The first stage - primary hemostasis, or prephase, seems to precede and trigger the second stage - coagulation itself, which, in turn, is a multiphase process. Its essence consists of chemical enzymatic reactions, as a result of which appear in the blood active substances- coagulation factors.

Primary hemostasis

It's complicated physiological process, occurring in several phases. Its main participants are the vessel wall, the nervous system and blood platelets. Primary hemostasis begins primarily with a primary vascular spasm of a reflex nature. Then the so-called endothelial-platelet reaction begins. At the site of injury, the vascular endothelium changes its charge. Platelets occupying an edge position in the vessel begin to adhere (stick) to the damaged surface of the vessel and agglutinate (stick together) with each other. As a result, after 2-3 minutes the third phase begins - the phase of formation of the “platelet nail”. During this phase, bleeding stops, but blood clotting has not yet occurred; blood plasma remains liquid. The resulting thrombus is loose, and within a short time the processes are reversible. The fourth phase is that in the formed thrombus morphological transformations of platelets begin, which will lead to their irreversible changes and destruction. This is a viscous metamorphosis of platelets. As a result of viscous metamorphosis, the clotting factors contained there are released from platelets. Their interaction leads to the appearance of traces of thrombin, which triggers a cascade of chemical enzymatic reactions- enzymatic coagulation.

Enzymatic coagulation

The appearance of traces of thrombin triggers a complex process of so-called enzymatic coagulation.

The first phase of enzymatic coagulation begins as a result of a multi-stage interaction of blood and tissue coagulation factors, when a previously absent factor, thromboplastin, appears in the blood. The second phase is the interaction of thromboplastin with prothrombin, an inactive precursor of thrombin. As a result of the interaction of thromboplastin and prothrombin in the presence of calcium salts, active thrombin appears in the blood in a concentration sufficient to begin the coagulation stage - the interaction of thrombin with soluble fibrinogen and the transition of the latter to insoluble fibrin. This is the third phase. By the appearance of the first fibrin threads in the clinic, the blood clotting time is determined.

Thus, the process of enzymatic blood coagulation occurs in three stages: 1 - the formation of active thromboplastin, 2 - the appearance of active thrombin and 3 - precipitation of insoluble fibrin filaments.

Then the next enzymatic stage begins, during which the blood clot thickens and contracts, separating the clear, liquid serum that has lost its ability to coagulate. This is the fourth stage of blood clotting - retraction (compression) of the blood clot. And finally, the last fifth stage begins - lysis (dissolution) of the blood clot. This is also a multi-stage process in which enzymatic interactions of many substances occur, ultimately leading to the appearance of the active enzyme - fibrinolysin. Fibrinolysin destroys the bonds between fibrin strands and converts it back into insoluble fibrinogen. Currently, it is customary to talk about the existence of an independent fibrinolytic system in the body. Of course, these processes in the body are much more complex, and many people take part in them. larger number factors.

Blood coagulation - the transition from a liquid state to a jelly-like clot - is a biologically important protective reaction of the body that prevents blood loss.

At the site of injury to a small blood vessel, a blood clot is created - a thrombus, which is like a plug that clogs the vessel and stops further bleeding. If the blood's ability to clot is reduced, even minor injuries can cause fatal bleeding.

Human blood released from the vessels begins to clot after 3-4 minutes, and after 5-6 minutes it completely turns into a gelatinous clot. If the inner membrane (intima) is damaged blood vessels and with increased blood clotting, blood clotting can also occur inside blood vessels in the whole body. In this case, a blood clot forms inside the vessel.

Blood clotting is based on a change in the physicochemical state of the protein contained in the plasma - fibrinogen. The latter passes from a soluble to an insoluble form, turning into fibrin and forming a clot.

Fibrin falls out in the form of long thin threads, forming networks in the loops of which formed elements are retained. If the blood released from the vessel is beaten with a panicle, then most of the resulting fibrin remains on the panicle. Fibrin, well washed from erythrocytes, has white and fibrous structure.

Blood from which fibrin has been removed in this way is called defibrinated. It consists of shaped elements and blood serum. Consequently, blood serum differs in composition from plasma in the absence of fibrinogen.

Serum can be separated from a blood clot by leaving a tube of clotted blood for a while. In this case, the blood clot in the test tube is compacted, tightened, and a certain amount of serum is squeezed out of it.

Rice. 2. Blood coagulation diagram.

Not only can it curl up whole blood, but also plasma. If you separate the plasma from the formed elements by centrifugation in the cold, which prevents blood clotting, and then warm the plasma to 20-35°, it will quickly clot.

A number of theories have been proposed to explain the mechanism of blood clotting. Currently, the enzymatic theory of blood coagulation, the foundations of which were laid almost a century ago by A. Schmidt, is generally accepted.

According to this theory, the final stage of coagulation is the transition of fibrinogen dissolved in plasma into insoluble fibrin under the influence of the enzyme thrombin (Fig. 2, stage III).

There is no thrombin in the circulating blood. It is formed from a blood plasma protein - prothrombin, synthesized by the liver. For the formation of thrombin, the interaction of prothrombin with thromboplastin is necessary, which must occur in the presence of calcium ions (Fig. 2, stage II).

There is also no thromboplastin in the circulating blood. It is formed when blood platelets are destroyed (blood thromboplastin) or tissue is damaged (tissue thromboplastin).

The formation of blood thromboplastin begins with the destruction of blood platelets and the interaction of the substances released with the globulin present in the blood plasma - factor V (its other name is accelerator globulin) and with another globulin in the blood plasma - the so-called antihemophilic globulin (its other name is thromboplastinogen), and also with another substance in the blood plasma - the so-called plasma component of thromboplastin (its other name is Christmas factor). In addition, the presence of calcium ions is also necessary for the formation of blood thromboplastin (see Fig. 2, stage I, left).

The formation of tissue thromboplastin occurs through the interaction of substances released from destroyed tissue cells with the already mentioned blood plasma globulin - factor V, as well as with blood plasma globulin - factor VII (its other name is proconvertin) and also necessarily in the presence of calcium ions (Fig. 2 , stage I, right). Once thromboplastin occurs, the process of blood clotting quickly begins.

The above diagram is far from complete, since in reality, much more different substances take part in the process of blood clotting.

In the absence of the above-mentioned antihemophilic globulin in the blood, which takes part in the formation of thromboplastin, a disease occurs - hemophilia, characterized by sharp reduced clotting blood. With hemophilia, even a small injury can lead to dangerous blood loss.

Developed chemical methods extracting thrombin from plasma and obtaining it in large quantities(B. A. Kudryashov). This drug significantly accelerates blood clotting. Thus, oxalate blood, in which thrombin is not formed due to calcium precipitation, coagulates in a test tube within 2-3 seconds after adding thrombin. If, when an organ is injured (for example, the liver, spleen, brain), the bleeding cannot be stopped by ligating the vessels, then applying gauze moistened with thrombin solution to their surface quickly stops the bleeding.

After fibrinogen transforms into fibrin, the resulting clot becomes denser, tightens, in other words, its retraction occurs. This process occurs under the influence of a substance called retractozyme, which is released during the breakdown of blood platelets. Experiments on rabbits have shown that with a sharp decrease in the number of blood platelets, blood clotting can occur, but the clot does not harden, and it remains loose, not providing good closure of the damaged blood vessel.

Blood clotting changes under the influence of the nervous system. Coagulation is accelerated by painful stimuli. Increasing blood clotting prevents blood loss. For irritation of the upper cervical sympathetic node The clotting time of blood is shortened, and when it is removed, it is lengthened.

Blood coagulation can also change conditionally. Thus, if a signal is repeatedly combined with painful stimulation, then under the influence of only one signal, which previously had no effect on blood coagulation, this process accelerates. One might think that when the nervous system is irritated, some substances are formed in the body that accelerate blood clotting. It is known, for example, that adrenaline, the release of which from the adrenal glands is stimulated nervous system and increases with painful stimulation and emotional states, increases blood clotting. At the same time, adrenaline constricts the arteries and arterioles and thereby also helps to reduce bleeding when blood vessels are injured. The adaptive significance of these facts is clear.

Row physical factors And chemical compounds inhibits blood clotting. In this regard, we should first of all note the effect of cold, which significantly slows down the blood clotting process.

Blood clotting is also slowed down if the blood is placed in a glass vessel whose walls are coated with paraffin or silicone, after which they are not wetted by the blood. In such a vessel, blood can remain liquid for several hours. Under these conditions, the destruction of blood platelets and the release into the blood of the substances they contain involved in the formation of thrombin are greatly hampered.

Oxalate and citric acid salts prevent blood clotting. When sodium citrate is added to the blood, calcium ions bind; Ammonium oxalate causes calcium to precipitate. In both cases, the formation of thromboplastin and thrombin becomes impossible. Oxalates and citrates are used only to prevent blood clotting outside the body. They cannot be introduced into the body in large quantities, since the binding of blood calcium in the body causes severe violations life activity.

Some substances, called anticoagulants, completely eliminate the possibility of blood clotting. These include heparin, isolated from lung and liver tissue, and hirudin, isolated from salivary glands leeches. Heparin interferes with the action of thrombin on fibrinogen and also inhibits the activity of thromboplastin. Hirudin has a depressing effect on the third stage of the blood coagulation process, i.e., it prevents the formation of fibrin.

There are also so-called anticoagulants indirect action. Without directly affecting the blood clotting process, they inhibit the formation of substances involved in this process. These include synthetically produced drugs - dicoumarin, pelentan, etc., which block the synthesis of prothrombin and factor VII in the liver.

Another substance was found in serum proteins - fibrinolysin, which dissolves the formed fibrin. This substance is an enzyme found in the blood plasma in an inactive form. Its precursor, profibrinolysin, is activated by fibrinokinase, which is found in many tissues of the body.

From all of the above it follows that there are two systems in the blood at the same time: coagulation and anticoagulation. Normally, they are in a certain balance, which prevents the processes of intravascular coagulation. This balance is disrupted by certain diseases and injuries.

The importance of the physiological anticoagulant system is shown in the experiments of B. A. Kudryashov. If an animal is quickly injected into a vein with a sufficient amount of thrombin, death occurs due to intravascular coagulation. If the same lethal dose When thrombin is introduced into the body slowly, the animal does not die, but its blood largely loses its ability to clot.

This led to the conclusion that the administration of thrombin causes the appearance of substances in the body that prevent blood clotting. The release of these substances is regulated by the nervous system. If you denervate one leg of a rat and slowly inject thrombin into its vein, the blood will clot only in the vessels of the denervated leg. It is believed that an increase in the level of thrombin in the vascular bed causes a reflex release of substances that prevent coagulation from the vessel wall. Transection of nerves, as well as exposure to narcotic substances, suppress this reflex.