Blood clotting: what is it, and what affects blood clotting? All phases of gradual blood coagulation How blood coagulation occurs in the human body

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 blood clot, which is like a plug that clogs the vessel and stops further bleeding. With a decrease in the ability of blood to clot, even minor wounds can cause fatal bleeding.

The human blood released from the vessels begins to coagulate after 3-4 minutes, and after 5-6 minutes it completely turns into a gelatinous clot. If the inner lining (intima) of the blood vessels is damaged and if blood coagulation is increased, blood coagulation can also occur inside the blood vessels in the whole organism. In this case, a thrombus forms inside the vessel.

The basis of blood coagulation is a change in the physicochemical state of the protein contained in the plasma - fibrinogen. The latter passes from a soluble form to an insoluble one, 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. Well washed from erythrocytes, fibrin has a white color and a fibrous structure.

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

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

Rice. 2. Scheme of blood coagulation.

Not only whole blood, but also plasma can coagulate. If the plasma is separated by centrifugation from the formed elements in the cold, which prevents blood clotting, and then the plasma is warmed to 20-35 °, then it will quickly clot.

A number of theories have been proposed to explain the mechanism of blood clotting. At present, the enzymatic theory of blood coagulation, the foundations of which were laid almost a century ago by A. Schmidt, enjoys general recognition.

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 thrombin enzyme (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. The formation of thrombin requires the interaction of prothrombin with thromboplastin, 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 platelets are destroyed (blood thromboplastin) or when tissues are damaged (tissue thromboplastin).

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

The formation of tissue thromboplastin occurs when substances released from destroyed tissue cells interact 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). After the occurrence of thromboplastin, the process of blood clotting quickly begins.

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

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 a sharply reduced blood clotting. With hemophilia, even a small wound can lead to dangerous blood loss.

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

After the transition of fibrinogen into fibrin, the resulting clot is compacted, contracted, in other words, it is retracted. This process is carried out under the influence of a substance called retractozyme, which is released during the breakdown of platelets. Experiments on rabbits have shown that with a sharp decrease in the number of platelets, blood coagulation can occur, but the clot does not thicken, 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. An increase in blood clotting at the same time prevents blood loss. When the upper cervical sympathetic node is irritated, the blood coagulation time is shortened, and when it is removed, it is lengthened.

Blood coagulation can also change conditioned reflex. So, if any signal is repeatedly combined with pain irritation, then under the action 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 by the nervous system and increases during painful stimuli 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.

A number of physical factors and chemical compounds inhibit blood clotting. In this regard, we should first of all note the effect of cold, which significantly slows down the process of blood coagulation.

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

Blood clotting is prevented by oxalate and citrate salts. When sodium citrate is added to the blood, calcium ions are bound; 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 calcium in the blood in the body causes severe impairment of vital activity.

Some substances, they are called anticoagulants, completely eliminate the possibility of blood clotting. These include heparin, secreted from lung and liver tissue, and hirudin, secreted from the salivary glands of 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, that is, it prevents the formation of fibrin.

There are also anticoagulants of the so-called indirect action. Without directly affecting the process of blood coagulation, they inhibit the formation of substances involved in this process. These include synthetic preparations - dicoumarin, pelentan, etc., blocking the synthesis of prothrombin and factor VII in the liver.

In the composition of serum proteins, another substance was found - 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 found in many body tissues.

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 blood coagulation. This balance is disturbed in certain diseases and injuries.

The value of the physiological anticoagulant system is shown in the experiments of B. A. Kudryashov. If a sufficient amount of thrombin is rapidly injected into an animal's vein, death occurs due to intravascular coagulation. If the same lethal dose of thrombin is introduced into the body slowly, then the animal does not die, but its blood loses its ability to coagulate to a large extent.

This led to the conclusion that the introduction 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 one paw is denervated in a rat and thrombin is slowly injected into its vein, then the blood will clot only in the vessels of the denervated paw. It is believed that an increase in the level of thrombin in the vascular bed causes a reflex release by the vessel wall of substances that prevent coagulation. Transection of nerves, as well as exposure to drugs, suppress this reflex.

One of the most important processes in our body is blood clotting. Its scheme will be described below (images are also provided for clarity). And since this is a complex process, it is worth considering it in detail.

How is it going?

So, the designated process is responsible for stopping the bleeding that occurred due to damage to one or another component of the vascular system of the body.

In simple terms, three phases can be distinguished. The first is activation. After damage to the vessel, successive reactions begin to occur, which ultimately lead to the formation of the so-called prothrombinase. It is a complex complex consisting of V and X. It is formed on the phospholipid surface of platelet membranes.

The second phase is coagulation. At this stage, fibrin is formed from fibrinogen - a high-molecular protein, which is the basis of blood clots, the occurrence of which implies blood clotting. The diagram below illustrates this phase.

And finally, the third stage. It implies the formation of a fibrin clot, which has a dense structure. By the way, it is by washing and drying it that it is possible to obtain a “material”, which is then used to prepare sterile films and sponges to stop bleeding caused by rupture of small vessels during surgical operations.

About reactions

The scheme was briefly described above, by the way, it was developed back in 1905 by a coagulologist named Paul Oskar Morawitz. And it has not lost its relevance to this day.

But since 1905, much has changed in understanding blood clotting as a complex process. With progress, of course. Scientists have been able to discover dozens of new reactions and proteins that are involved in this process. And now the cascade pattern of blood coagulation is more common. Thanks to her, the perception and understanding of such a complex process becomes a little more understandable.

As you can see in the image below, what is happening is literally “broken into bricks”. It takes into account the internal and external system - blood and tissue. Each is characterized by a certain deformation that occurs as a result of damage. In the blood system, damage is done to the vascular walls, collagen, proteases (splitting enzymes) and catecholamines (mediator molecules). In the tissue, cell damage is observed, as a result of which thromboplastin is released from them. Which is the most important stimulator of the coagulation process (otherwise called coagulation). It goes directly into the blood. This is his "way", but it has a protective character. After all, it is thromboplastin that starts the clotting process. After its release into the blood, the implementation of the above three phases begins.

Time

So, what exactly is blood coagulation, the scheme helped to understand. Now I would like to talk a little about time.

The whole process takes a maximum of 7 minutes. The first phase lasts from five to seven. During this time, prothrombin is formed. This substance is a complex type of protein structure responsible for the course of the coagulation process and the ability of blood to thicken. Which is used by our body in order to form a blood clot. It clogs the damaged area, so that the bleeding stops. All this takes 5-7 minutes. The second and third stages happen much faster. For 2-5 seconds. Because these phases of blood clotting (diagram provided above) affect processes that occur everywhere. And that means at the site of damage directly.

Prothrombin, in turn, is formed in the liver. And it takes time to synthesize it. How quickly a sufficient amount of prothrombin is produced depends on the amount of vitamin K contained in the body. If it is not enough, the bleeding will be difficult to stop. And this is a serious problem. Since the lack of vitamin K indicates a violation of the synthesis of prothrombin. And this is a disease that needs to be treated.

Synthesis stabilization

Well, the general scheme of blood clotting is clear - now we should pay a little attention to the topic of what needs to be done to restore the required amount of vitamin K in the body.

For starters, eat right. The largest amount of vitamin K is found in green tea - 959 mcg per 100 g! Three times more, by the way, than in black. That is why it is worth drinking it actively. Do not neglect vegetables - spinach, white cabbage, tomatoes, green peas, onions.

Vitamin K is also found in meat, but not in everything - only in veal, beef liver, lamb. But least of all it is in the composition of garlic, raisins, milk, apples and grapes.

However, if the situation is serious, then it will be difficult to help with just a variety of menus. Usually, doctors strongly recommend combining your diet with the drugs they have prescribed. Treatment should not be delayed. It is necessary to start it as soon as possible in order to normalize the mechanism of blood coagulation. The treatment regimen is prescribed directly by the doctor, and he is also obliged to warn what can happen if the recommendations are neglected. And the consequences can be liver dysfunction, thrombohemorrhagic syndrome, tumor diseases and damage to bone marrow stem cells.

Schmidt's scheme

At the end of the 19th century, there lived a famous physiologist and doctor of medical sciences. His name was Alexander Alexandrovich Schmidt. He lived for 63 years, and devoted most of his time to the study of problems of hematology. But especially carefully he studied the topic of blood coagulation. He managed to establish the enzymatic nature of this process, as a result of which the scientist proposed a theoretical explanation for it. Which clearly depicts the scheme of blood coagulation provided below.

First of all, the damaged vessel is reduced. Then, at the site of the defect, a loose, primary platelet plug is formed. Then it gets stronger. As a result, a red blood clot (otherwise referred to as a blood clot) is formed. After which it partially or completely dissolves.

During this process, certain blood clotting factors are manifested. The scheme, in its expanded version, also displays them. They are denoted by Arabic numerals. And there are 13 of them in total. And you need to tell about each.

Factors

A complete blood coagulation scheme is impossible without listing them. Well, it's worth starting from the first.

Factor I is a colorless protein called fibrinogen. Synthesized in the liver, dissolved in plasma. Factor II - prothrombin, which has already been mentioned above. Its unique ability lies in the binding of calcium ions. And it is precisely after the breakdown of this substance that the coagulation enzyme is formed.

Factor III is a lipoprotein, tissue thromboplastin. It is commonly called the transport of phospholipids, cholesterol, and also triacylglycerides.

The next factor, IV, are Ca2+ ions. The ones that bind under the influence of a colorless protein. They are involved in many complex processes, in addition to clotting, in the secretion of neurotransmitters, for example.

Factor V is a globulin. Which is also formed in the liver. It is necessary for the binding of corticosteroids (hormonal substances) and their transport. Factor VI existed for a certain time, but then it was decided to remove it from the classification. Since scientists have found out - it includes factor V.

But the classification did not change. Therefore, V is followed by factor VII. Includes proconvertin, with the participation of which tissue prothrombinase is formed (first phase).

Factor VIII is a protein expressed in a single chain. It is known as antihemophilic globulin A. It is because of its lack that such a rare hereditary disease as hemophilia develops. Factor IX is "related" to the previously mentioned. Since it is antihemophilic globulin B. Factor X is directly a globulin synthesized in the liver.

And finally, the last three points. These are the Rosenthal, Hageman factor and fibrin stabilization. Together, they affect the formation of intermolecular bonds and the normal functioning of such a process as blood coagulation.

Schmidt's scheme includes all these factors. And it is enough to get acquainted with them briefly in order to understand how the described process is complex and ambiguous.

Anti-clotting system

This concept also needs to be noted attention. The blood coagulation system was described above - the diagram also clearly demonstrates the course of this process. But the so-called "anti-coagulation" also has a place to be.

To begin with, I would like to note that in the course of evolution, scientists solved two completely opposite tasks. They tried to find out - how does the body manage to prevent blood from flowing out of damaged vessels, and at the same time keep it in a liquid state in its entirety? Well, the solution to the second problem was the discovery of an anticoagulant system.

It is a specific set of plasma proteins that can slow down the rate of chemical reactions. That is to inhibit.

And antithrombin III is involved in this process. Its main function is to control the work of some factors that include the scheme of the blood coagulation process. It is important to clarify: it does not regulate the formation of a blood clot, but eliminates unnecessary enzymes that have entered the bloodstream from the place where it is formed. What is it for? To prevent the spread of clotting to areas of the bloodstream that have been damaged.

obstructing element

Talking about what the blood coagulation system is (the scheme of which is presented above), one cannot but note such a substance as heparin. It is a sulfur-containing acidic glycosaminoglycan (one of the types of polysaccharides).

It is a direct anticoagulant. A substance that contributes to the inhibition of the activity of the coagulation system. It is heparin that prevents the formation of blood clots. How does this happen? Heparin simply reduces the activity of thrombin in the blood. However, it is a natural substance. And it is beneficial. If this anticoagulant is introduced into the body, then it is possible to contribute to the activation of antithrombin III and lipoprotein lipase (enzymes that break down triglycerides - the main sources of energy for cells).

Now, heparin is often used to treat thrombotic conditions. Only one of its molecules can activate a large amount of antithrombin III. Accordingly, heparin can be considered a catalyst - since the action in this case is really similar to the effect caused by them.

There are other substances with the same effect contained in Take, for example, α2-macroglobulin. It contributes to the splitting of the thrombus, affects the process of fibrinolysis, performs the function of transport for 2-valent ions and some proteins. It also inhibits substances involved in the clotting process.

Observed changes

There is one more nuance that the traditional blood coagulation scheme does not demonstrate. The physiology of our body is such that many processes involve not only chemical changes. But also physical. If we could observe clotting with the naked eye, we would see that the shape of the platelets changes in the process. They turn into rounded cells with characteristic spiny processes, which are necessary for the intensive implementation of aggregation - the combination of elements into a single whole.

But that's not all. During the clotting process, various substances are released from platelets - catecholamines, serotonin, etc. Because of this, the lumen of the vessels that have been damaged narrows. What causes functional ischemia. The blood supply to the injured area is reduced. And, accordingly, the outpouring is also gradually reduced to a minimum. This gives the platelets the opportunity to cover the damaged areas. They, due to their spiny processes, seem to be “attached” to the edges of the collagen fibers that are located at the edges of the wound. This ends the first, longest activation phase. It ends with the formation of thrombin. This is followed by a few more seconds of the phase of coagulation and retraction. And the last stage is the restoration of normal blood circulation. And it matters a lot. Since the full healing of the wound is impossible without a good blood supply.

Good to know

Well, something like this in words and looks like a simplified scheme of blood coagulation. However, there are a few more nuances that I would like to note with attention.

Hemophilia. It has already been mentioned above. This is a very dangerous disease. Any hemorrhage by a person suffering from it is experienced hard. The disease is hereditary, develops due to defects in the proteins involved in the coagulation process. It can be detected quite simply - with the slightest cut, a person will lose a lot of blood. And it will take a lot of time to stop it. And in especially severe forms, hemorrhage can begin for no reason. People with hemophilia can become disabled early. Since frequent hemorrhages in muscle tissue (usual hematomas) and in joints are not uncommon. Is it curable? With difficulties. A person should literally treat his body as a fragile vessel, and always be careful. If bleeding occurs, donated fresh blood containing factor XVIII should be urgently administered.

Men usually suffer from this disease. And women act as carriers of the hemophilia gene. Interestingly, the British Queen Victoria was one. One of her sons contracted the disease. The other two are unknown. Since then, hemophilia, by the way, is often called the royal disease.

But there are also reverse cases. Meaning If it is observed, then a person also needs to be no less careful. Increased clotting indicates a high risk of intravascular thrombosis. Which clog entire vessels. Often the consequence can be thrombophlebitis, accompanied by inflammation of the venous walls. But this defect is easier to treat. Often, by the way, it is acquired.

It's amazing how much happens in the human body when he cuts himself with a piece of paper. You can talk for a long time about the features of blood, its coagulation and the processes that accompany it. But all the most interesting information, as well as diagrams that clearly demonstrate it, are provided above. The rest, if desired, can be viewed individually.

When tissue is injured, damage to the smallest or large blood vessels occurs, bleeding begins. In such cases, the blood coagulation system begins to act. Coagulation - the transformation of liquid blood into an elastic clot as a result of the transition of fibrinogen protein dissolved in plasma into insoluble fibrin when blood flows out of a damaged vessel. The main functions of blood include: transport and protective. The ability to coagulate can also be attributed to the protective function. Due to this ability, in case of damage to the external integument or internal tissues of the body, it is possible to block the site of damage with a thrombus, which also prevents the penetration of pathogens into the body. Rapid blood clotting speeds up the start of the wound healing process.

Usually blood clotting occurs within 5-7 minutes. If the blood clots too long or does not clot at all, hemophilia may be suspected. If the blood coagulates too quickly, then there is a risk of embolism, myocardial infarction or stroke (all of these diseases can cause blood clots to form in the vessels).

As a result of blood coagulation, dense formations appear (the process resembles the curdling of milk). Dense formations of blood form a plug (thrombus), which clogs the wound, preventing bleeding. At the same time, the muscles of the blood vessels contract, the torn edges of which are pulled inward. So the blood vessels close even tighter. Approximately 20 min. this contraction is gone. If the blood didn't clot, the bleeding would start again.

Blood coagulates under the influence of various factors, which are called blood clotting factors. First of all, it is the air that affects external wounds. The clotting process can also cause irregularities in the walls of blood vessels and their sharp edges. Then the platelets contained in the blood at the site of injury activate the enzyme thrombin (coagulating factor).

Under the influence of thrombin and calcium, which is always present in the blood, fibrinogen, a protein dissolved in blood plasma, is converted into fibrin (fibrous substance). Long elastic threads of fibrin form a dense thread ball (clot).

Various formed elements of the blood enter the formed clot, forming a kind of patch. With the formation of clots and wound healing, the fibrin strands are compressed and push the blood serum out of the clot. The clot becomes sufficiently dense and able to protect the wound from infection. As the wound heals, the fibrin clot dissolves and dissolves.

In order for thrombin to cause clotting, a chemical chain reaction must occur in the human body, which involves about 30 different chemicals, including the aforementioned enzymes and calcium. The main reaction is the conversion of prothrombin (the primary substance) into thrombin, an enzyme that causes blood clotting. Plasma initially contains only prothrombin. This prevents spontaneous folding. For the formation of thrombin from prothrombin, 12 factors are necessary. With a lack of at least one of these factors, a chain reaction does not occur, and the blood does not clot.

Blood clotting is a process that occurs in the human body and involves a change in the structure of blood cells, that is, the transformation from a liquid state to a jelly-like state. In the event of a minor cut or other wound, the resulting skin lesions heal quickly. This fact is good for everyone. Yet none of us has ever thought about the most important question. It is necessary to know the details of the wound healing process, or rather, where does the blood coagulation process begin, what is its essence and what place does it occupy in the life of each person?

In medicine, there is also another concept of the blood coagulation system, namely hemostasis. We can say that hemostasis is a process that is responsible for the liquid state of blood in the vessels of the human body. It also prevents the development of extensive blood loss. In many medical sources, you can find information that 5 liters of blood cells move in all vessels in the body. Therefore, when the skin or blood vessels are damaged, blood can be shed, and if not the coagulation system, then each person could die from blood loss. Thus, blood coagulation is regulated.

The blood hemostasis system itself is unique in that it keeps the blood fluid throughout the numerous arteries and veins in the human body. If even the smallest vessel is damaged, the active work of special enzymes immediately begins, which gradually tightens the hole, preventing the outflow of blood cells. It is easier to describe this process as the formation of blood clots, that is, blood cells begin to stick together.

As a rule, blood coagulates due to the existence of a certain system in the human body, which refers to the formation of clotting inhibitors. The enzyme that promotes the process of coagulation is always formed in the body. And inhibitors are constantly working. The work of inhibitors can be divided into 2 main phases:

the action of heparin and antiprothrombinase begins;
the work of thrombin inhibitors (fibrin, fibrinogen, prethrombin I and II) begins.

If a person becomes ill, then other inhibitors can be formed in the body. Since at high temperatures, intensive clotting begins.

In addition to the blood coagulation system, there is also an anti-coagulation system. The anticoagulant system begins to function when thrombin begins to irritate the chemoreceptors of blood vessels. Thus, fibrinogen, which is the main factor in the formation of blood clots, is destroyed. The anticoagulant system is very important for the full functioning of the body.

What enzyme promotes coagulation?

If the mechanism of blood clotting is clear, now we need to find out which enzyme contributes to blood clotting? The main enzyme involved in the coagulation process is thrombin. During the course of chemical reactions in the body, this substance acts on fibrinogen, converting it into fibrin. This substance also regulates fibrinolysis and the formation of blood clots, maintains vascular tone.

This enzyme is formed during inflammatory processes occurring in the body at high temperatures.

Then the next stage of coagulation begins, thrombin is formed from prothrombin. In turn, thrombin activates coagulation factors V, VIII, XIII. The hormonal properties of the substance in question are manifested in close contact with the endothelium and platelets. But in the process of docking with thrombomodulin, the action of blood clotting ends.

The role of thrombin in coagulation

The key function of hemostasis is to block a rupture in the vessel. In this case, fibrin filaments form a thrombus, after which the blood cells acquire a characteristic astringent property. So, what enzyme is involved in coagulation? This is thrombin, which comes from the word "thrombus". Thrombin is in constant readiness, and as soon as damage to the vessel wall occurs, its active work begins.

There are the following phases of blood coagulation:

Stage I - the beginning, the appearance of prothrombinase. At the first stage, the formation of tissue and blood enzymes occurs, while the process of their formation takes place at different rates. The important thing here is that the tissue enzyme activates the work of the blood enzyme.
Stage II - thrombin is formed. Prothrombin begins to disintegrate into particles, after disintegration, a substance is formed that activates thrombin.
Stage III - the formation of fibrin. At this stage, the enzyme involved in coagulation begins to act on fibrinogen, while amino acids are cleaved off.
Stage IV. It is one of the special ones, because fibrin polymerization begins and a blood clot forms.
Stage V - fibrinolysis occurs. This is the final stage of hemostasis, as complete blood clotting occurs.

The listed stages of the hemostasis system indicate a close and interconnected process. The norm of clotting is considered to be a period of 7 to 12 minutes, tests are evaluated at room temperature. All the stages described can be depicted schematically with a certain sequence.

It should be noted that the division of coagulation by type, that is, into external and internal, is considered conditional, and can only be used among scientists for simplicity and convenience, since both types of blood coagulation are interconnected.

What affects clotting

The process of coagulation occurs due to certain substances, which are called factors. Otherwise, they can be called "plasma proteins". Agents that are actively involved in the process of hemostasis are:

fibrin and fibrinogen;
prothrombin and thrombin;
thromboplastin;
ionized calcium (Ca++);
proaccelerin and accelerin;
Koller factor;
Hageman factor;
fibrin stabilizer Lucky-Loranda.

The action of all of the above is the correct coagulation, despite the fact that this process is quite fast. They help prevent the development of extensive blood loss in violation of the vascular wall.

How does the process of hemostasis occur?

It is important to know that a damaged vessel is not repaired in any random way. Numerous enzymes are involved in the process of coagulation, each performing its assigned function. The very essence of this process lies in the fact that active folding of proteins and erythrocytes begins. In this case, blood clots attach to the wall of the damaged artery and their further detachment is impossible.

In case of damage to the vessels, substances begin to be released from them that inhibit the entire coagulation process. Platelets begin to change and break down, and then thromboplastin and thrombin enter the bloodstream. Then, under the influence of thrombin, fibrinogen is converted into fibrin (it is a thread mesh). It is the mesh of fibrin threads that is located in the damaged area and becomes denser for some time. Consequently, the coagulation process is completed, and the blood from the damaged vessel stops.

It is also important to know how long coagulation should take place at normal body temperature. The norm of blood clotting, starting from damage to the vascular wall and up to a complete stop of blood, is usually an interval of 2-4 minutes at normal body temperature. However, thrombin coagulates the blood within 10 minutes. It is this time that is considered the norm for coagulation. The coagulation process may slow down or not end at all. Blood may not clot if there are diseases such as hemophilia or diabetes. The blood coagulation scheme is not simple, and for proper coagulation it is important to monitor your health, regularly donate blood for analysis in order to avoid major bleeding in emergency cases.

Blood moves in our body through the blood vessels and has a liquid state. But in case of 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 closes, and thereby stops the bleeding. The wound heals over time. Otherwise, if the blood coagulation process is disturbed for any reason, a person may die even from minor damage.

Why does blood clot?

Blood clotting is a very important protective reaction of the human body. It prevents the loss of blood, while maintaining the constancy of its volume 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, falling out in the form of thin threads. These very threads can form a dense network with small cells, which delays the uniform elements. This is how a thrombus is formed. Over time, the blood clot gradually thickens, tightens the edges of the wound and thereby contributes to its speedy healing. When compacted, the clot secretes a yellowish clear liquid called serum.

Platelets are also involved in blood clotting, which thicken the clot. This process is similar to getting cottage cheese from milk, when casein (protein) is folded and whey is also formed. The wound in the healing process contributes to the gradual resorption and dissolution of the fibrin clot.

How is the folding process started?

A. A. Schmidt in 1861 found out that the process of blood coagulation 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.

In humans, there is always a little thrombin in the blood, which is in an inactive state, prothrombin, as it is also called. Prothrombin is formed in the human liver and converted to active thrombin under the influence of thromboplastin and calcium salts present in plasma. It must be said that thromboplastin is not contained in the blood, it is formed only in the process of destruction of platelets and damage to other cells of the body.

The occurrence of thromboplastin is a rather complex process, since, in addition to platelets, some proteins contained in the plasma are involved in it. In the absence of individual 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 develops (or, in other words, bleeding). Those people who live with this disease can lose significant amounts of blood due to even a small scratch.

Phases of blood clotting

Thus, blood clotting is a stepwise process that consists of three phases. The first is considered the most difficult, during which the formation of a complex compound of 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, turns it into active thrombin. And in the final third phase, thrombin, in turn, affects fibrinogen (a protein that is dissolved in blood plasma), turning it into fibrin, an insoluble protein. That is, with the help of coagulation, the blood passes from a liquid to a jelly-like state.

Types of blood clots

There are 3 types of blood clots or thrombi:

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

clotting factors

Thrombus formation is a very complex process involving numerous proteins and enzymes found in blood plasma, platelets and tissues. These are the clotting factors. Those of them that are contained in the plasma are usually denoted by Roman numerals. Arabic indicates platelet factors. In the human body, there are all blood coagulation factors that are in an inactive state. When a vessel is damaged, a rapid successive activation of all of them occurs, as a result of which the blood coagulates.

blood clotting, normal

In order to determine whether the blood is clotting normally, a study is carried out, which is called a coagulogram. It is necessary to make such an analysis if a person has thrombosis, autoimmune diseases, varicose veins, acute and chronic bleeding. It is also mandatory for pregnant women and those who are preparing for surgery. For this kind of study, blood is usually taken from a finger or a vein.

Blood clotting time is 3-4 minutes. After 5-6 minutes, it completely collapses and becomes a gelatinous clot. As for the 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 constituent of thrombin. Its norm is 78-142%.

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

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

Fibrinogen is a plasma protein, it is responsible for the formation of a blood clot, 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 thrombus.

The two systems of our body

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

It is known that two systems coexist in the human body. One contributes to the speedy coagulation of blood, while the second in every way prevents this. If both of these systems are in balance, then the blood will coagulate with external damage to the vessels, and inside them it will be liquid.

What promotes blood clotting?

Scientists have proven that the nervous system can influence the process of blood clot formation. So, the time of blood clotting decreases with painful irritations. Conditioned reflexes may also have an effect on clotting. A substance such as adrenaline, which is secreted from the adrenal glands, contributes to the speedy 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 are also involved in blood clotting. They help speed up this process, but there is another system in the body that prevents it.

What prevents blood from clotting?

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

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

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

Clotting in newborns

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