Blood coagulation. Factors, blood clotting time
The 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 sufficiently short period of time, which is called a blood clot or “blood clot”. With the help of a blood clot, the wound closes and bleeding stops. The wound heals over time. Otherwise, if the blood clotting process is disturbed for any reason, a person may die even from minor damage.
Why does blood clot?
Blood coagulation is a very important protective reaction of the human body. It prevents blood loss, while maintaining the constancy of its volume, located in the body. The coagulation mechanism is triggered by changing the physicochemical state of the blood, which is based on the protein fibrinogen dissolved in its plasma.
Fibrinogen is able to turn into insoluble fibrin,drop down in the form of thin threads. These same threads can form a dense network with small cells, which retains shaped elements. This is how a blood clot turns out. 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 coagulation, which condense the clot. This process is similar to the production of cottage cheese from milk when casein (protein) is rolled up and whey is also formed. The wound in the healing process contributes to the gradual resorption and dissolution of the fibrin clot.
How does the process of coagulation start?
AA 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.
A person in the blood constantly has a little thrombin, 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 by the action of thromboplastin and calcium salts present in the 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 in case of damage to other cells of the body.
The occurrence of thromboplastin is a rather complicated process, since in addition to platelets, some of the proteins contained in the plasma are involved. In the absence of individual proteins in the blood, blood coagulation may be slowed down or not occur at all. For example, if one of the globulins is lacking in plasma, then the well-known hemophilia disease (or on the other, bleeding) develops. Those people who live with this disease can lose significant amounts of blood due to even a small scratch.
Thus, blood coagulation is a phased process that consists of three phases. The first is considered the most difficult, during which the formation of the complex compound of thromboplastin occurs. In the next phase, thromboplastin and prothrombin (an inactive plasma enzyme) are necessary for blood coagulation.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, blood passes from a liquid to a jelly-like state.
Types of blood clots
There are 3 types of blood clots or blood clots:
- 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).
- In the capillaries (very small vessels) disseminated fibrin deposits are formed. This is the second type of blood clots.
- And the latter are red blood clots. They appear in places of slow blood flow and with the mandatory absence of changes in the vessel wall.
Blood coagulation factors
The formation of a blood clot is a very complex process, it involves numerous proteins and enzymes that are found in the blood plasma, platelets and tissue. These are coagulation 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 factors of blood clotting, which are in an inactive state. When a vessel is damaged, they are all quickly activated in succession; as a result, blood clots.
In order to determine whether the blood coagulates normally, a study is called a coagulogram. To make such an analysis is necessary if a person has thrombosis, autoimmune diseases, varicose veins, acute and chronic bleeding. Also, be sure to pass it pregnant women and those who are preparing for surgery. For this kind of research, blood is usually taken from a finger or vein.
Blood coagulation 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 in 1.5-2 minutes, and ends already after 2.5-5 minutes.
Blood clotting rates
Prothrombin is a protein that is responsible for blood clotting and is an important constituent element of thrombin. Its rate is 78-142%.
The 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 rate 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. With this indicator, it is possible to diagnose DIC, hemophilia and monitor the blood condition while 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 report inflammation in the body. In adults, its content should be 2.00-4.00 g / l, while in newborns it should be 1.25-3.00 g / l.
Antithrombin is a specific protein that provides resorption of a formed blood clot.
Two systems of our body
Of course, when bleeding is very important fast blood clotting, to reduce blood loss to zero. She herself must always remain in a liquid state.But there are pathological conditions that lead to blood coagulation inside the vessels, and this represents a greater danger to humans than bleeding. Diseases such as thrombosis of coronary heart vessels, pulmonary artery thrombosis, cerebral thrombosis, 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, the second in every way impede it. If both of these systems are in equilibrium, then the blood will coagulate with external damage to the vessels, and inside them will be liquid.
What contributes to blood clotting?
Scientists have shown that the nervous system can influence the process of blood clot formation. Thus, the blood clotting time is reduced with pain stimuli. Conditioned reflexes can also affect coagulation. Such a substance as adrenaline, which is released from the adrenal glands, contributes to the early clotting of blood. At the same time, it is able to make arteries and arterioles narrower and thus reduce possible blood loss.Vitamin K and calcium salts are also involved in blood coagulation. They help the speedy process of 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 does not form thromboplastin. It is known that the content of heparin in young men and teenagers after work decreases by 35-46%, but in adults it does not change.
Blood serum contains a protein called fibrinolysin. He is involved in the dissolution of fibrin. It is known that pain of medium strength can accelerate clotting, but severe pain slows down this process. Prevents blood clotting low temperature. The optimum is considered the body temperature of a healthy person. In the cold blood clots slowly, sometimes this process does not occur at all.
Increase the clotting time can salts of acids (citric and oxalic), precipitating the necessary for the rapid folding of calcium salts, as well as hirudin, fibrinolysin, sodium citrate and potassium. Medical leeches can produce with the help of the cervical glands a special substance - hirudin, which has an anticoagulant effect.
Coagulability in newborns
In the first week of a newborn's life, the coagulation of his blood occurs very slowly, but already during the second week, indicators of the level of prothrombin and all clotting factors approach the normal adult level (30-60%). Already 2 weeks after the birth of fibrinogen in the blood greatly increases and becomes like an adult. By the end of the first year of life in a child, the content of the remaining blood coagulation factors approaches that of an adult. They reach the norm by 12 years.