The idea of hemostasis is used to refer to the interruption of bleeding , whether by chemical means, physical means, or spontaneously. A hemorrhage, on the other hand, is the flow of blood that is generated when a blood vessel breaks.
Hemostasis, therefore, is a mechanism that causes the arrest of a hemorrhagic process . Thanks to hemostasis, blood stops flowing and remains in the blood vessels.
Normally, blood can circulate freely through the vessels. If a vessel ruptures, hemorrhage occurs (blood leaks out of the vessel). What hemostasis does is, at first, form a clot so that the bleeding stops. The body then takes care of repairing the damage and, finally, dissolves the clot. In this way the blood returns to circulate normally through the blood vessels.
If we analyze this process in detail, we will find that hemostasis consists of several phases . It begins with reflex vasoconstriction , an immediate transient response to damage to a blood vessel generated by the sympathetic nervous system (one of the parts of the autonomic nervous system; it is responsible for regulating various actions, such as the contraction of certain muscles. and the secretion of various glands).
Reflex vasoconstriction results in vascular spasm that reduces the diameter of the vessel and thus delays bleeding. On the other hand, it promotes the movement of blood cells , bringing them closer to the site of injury to facilitate the interaction between the subendothelium and platelets.
The second phase of hemostasis is called primary hemostasis . This is the process by which the "platelet plug" is formed, and it begins a few seconds later than the vascular trauma. Its formation takes place due to the force with which the platelets stick to the free collagen of the damaged vessel and the release of various chemical substances that increase the aggregation of the platelets, which favors the union between the different elements.
Thirdly we have secondary hemostasis , which in everyday speech is known as coagulation . It occurs because the chemical change that fibrinogen undergoes makes it insoluble and allows it to intertwine with other molecules of the same type to give rise to large macromolecular aggregates that join together in a three-dimensional network. Once it is transformed, fibrinogen is called fibrin .
This coagulation process is of a complex enzymatic type and involves the transformation of the fibrogen and its subsequent polymerization and cross-linking. It is important to note that clot formation does not always occur correctly, but sometimes certain alterations occur that cause delayed bleeding, such as hematomas.
The last phase of the hemostasis process is called fibrinolysis and consists of the disintegration of the clot formed in the previous one. Once the healing process begins, the cells responsible for forming new tissue reach the clot and little by little degrade it. The name of this phase refers to the aforementioned fibrin, which is precisely the component that keeps the clot attached to the vascular wall. The enzyme that catalyzes fibrinolysis is called plasmin , a serine that is produced from an inactive precursor called plasminogen and can be activated by different factors, such as coagulation.
It should be noted that hemostasis can be induced with drugs or by manual compression of the wound , for example. Thus, people are in a position to act against hemorrhage beyond the spontaneous action of the body.