Useful or harmful blood clotting?

With the phenomenon of blood coagulation is familiar from my own experience every person. How many times, damaging the skin, we look forward to the blood quickly curled up and stopped the bleeding. If the blood did not possess this remarkable property, people would die from the slightest scratch. It is always a danger for people suffering from disease hemophilia, in which the blood loses its ability to shrink. Given the enormous value blood for the body's clotting her, contributing to the closing of the bleeding vessels, is of great biological importance.
Knowledge of the mechanisms of blood coagulation is very important for science. It is often necessary to speed up the process of coagulation. Sometimes, on the contrary, we should be able to save the blood of Nesterovskaya (say, at the stations of blood transfusion). In some diseases of the blood can be folded inside blood vessels, forming the so-called clot - lumps to seal a particular vessel, often supplying vital organ, such as heart or brain. Therefore, in many cases, it is important to reduce the coagulation. In order to influence a particular phenomenon, it is necessary, of course, know his laws.
The mechanism of blood clotting is very complicated. We'll cover only the main regularities.
Among the plasma proteins has protein fibrinogen, which can come out of solution in the form of threads - there is its transformation into fibrin (from lat. fibra - fiber). In these threads delayed blood cells and forms a clot, blood clot. Therefore, the basis of coagulation is the conversion of fibrinogen to fibrin. Under normal conditions, the transformation is in the blood occurs so slowly that almost the result equal to zero. Why loss of fibrin is accelerated when wounded skin? The acceleration of the formation of a clot, blood clot is under the influence of the enzyme thrombin, which appears when vicodinii blood from the damaged vessel. Where does thrombin? Indeed, in normal circumstances it is not, otherwise the blood coagulated and would in vessels.
Among the plasma proteins in addition fibrinogen available in insignificant quantities specific protein produced by the liver prothrombin, which goes into thrombin under the influence of two factors: first, ions of calcium, which is always present in the plasma, secondly, a special enzyme thrombogenesis. This enzyme and is contained in blood platelets and released when their destruction. Once the blood instead of the smooth blood vessels in contact with a rough surface of damaged tissues, fragile blood platelets instantly start to collapse. Appears tromboksana, which together with ions of calcium converts prothrombin into thrombin. This concludes the first, preparatory phase of clotting process. Thrombin effect on fibrinogen and "roll" it: this is the second main phase of the process. Consequently, tromboksana is "enzyme enzyme". In patients with hemophilia, along with other violations include excessive resistance, "strength" of blood platelets. So trombolizisa released too sluggish, and the clotting process slows down sharply.
No matter how difficult outlined above scheme of the events playing out in blood coagulation, it reflects only the core elements of the process, only the "skeleton" of it. The coagulation system contains a number of additional links, the description of which would take a whole Chapter. In addition, the body has multi-component and multi-stage anti-clotting system. These normal hard interact and balance each other. For violations of such equilibrium violation occurs in the reduction of coagulation (bleeding)and increase of its (blood clots in the veins).
For example, first we considered the difficult process of blood clotting, we are immediately faced with contradictory phenomena characterizing the Symphony of life. Coagulation - protective phenomenon. From this point of view it should certainly be considered useful. However, it also may cause clogging of blood vessels in the heart or brain, cause myocardial infarction or stroke (bleeding into the brain). So the question, it is helpful or harmful blood clotting, cannot be answered unambiguously. Any Symphony contains and harmonious chords, consonances, and discordant - dissonances. Similarly, the Symphony of life includes phenomena that can be both helpful and harmful. Everything depends on specific conditions. Fairly popular wisdom says: there is no good without evil, good without bad.