- How hemostasis happens
- 1. Primary hemostasis
- 2. Secondary hemostasis
- 3. Fibrinolysis
- How to identify changes in hemostasis
Hemostasis corresponds to a series of processes that take place inside the blood vessels that aim to keep the blood fluid, without the formation of clots or hemorrhage.
Didactically, hemostasis occurs in three stages that happen in a fast and coordinated way and mainly involves platelets and proteins responsible for coagulation and fibrinolysis.
How hemostasis happens
Hemostasis occurs didactically in three stages that are dependent and occur simultaneously.
1. Primary hemostasis
Hemostasis begins as soon as the blood vessel is damaged. As a response to the injury, vasoconstriction of the injured vessel occurs in order to decrease local blood flow and thus prevent bleeding or thrombosis.
At the same time, platelets are activated and adhere to the vessel endothelium by means of von Willebrand factor. Then the platelets change their shape so that they can release their content in the plasma, which has the function of recruiting more platelets to the lesion site, and start to adhere to each other, forming the primary platelet plug, which has a temporary effect.
Learn more about platelets and their functions.
2. Secondary hemostasis
At the same time as primary hemostasis occurs, the coagulation cascade is activated, causing the proteins responsible for coagulation to be activated. As a result of the coagulation cascade, fibrin is formed, which has the function of strengthening the primary platelet plug, making it more stable.
Coagulation factors are proteins that circulate in the blood in its inactive form, but are activated according to the needs of the organism and have as their final objective the transformation of fibrinogen into fibrin, which is essential for the blood stagnation process.
3. Fibrinolysis
Fibrinolysis is the third stage of hemostasis and consists of the process of gradually destroying the hemostatic plug to restore normal blood flow. This process is mediated by plasmin, which is a protein derived from plasminogen and whose function is to degrade fibrin.
How to identify changes in hemostasis
Changes in hemostasis can be detected through specific blood tests, such as:
- Bleeding time (TS): This test consists of checking the time when hemostasis occurs and can be done through a small hole in the ear, for example. Through the result of bleeding time, it is possible to assess primary hemostasis, that is, whether the platelets have adequate function. Despite being a widely used test, this technique can cause discomfort, especially in children, since it is necessary to make a small hole in the ear and has a low correlation with the person's bleeding tendency; Platelet aggregation test: Through this test, it is possible to verify the platelet aggregation capacity, being also useful as a way to assess primary hemostasis. The person's platelets are exposed to various substances capable of inducing coagulation and the result can be observed in a device that measures the degree of platelet aggregation; Prothrombin time (PT): This test assesses the blood's ability to coagulate by stimulating one of the coagulation cascade pathways, the extrinsic pathway. Thus, it checks how long it takes the blood to generate the secondary hemostatic plug. Understand what the Prothrombin Time exam is and how it is done; Activated Partial Thromboplastin Time (APTT): This test also assesses secondary hemostasis, however it checks the functioning of the coagulation factors present in the intrinsic pathway of the coagulation cascade; Dosage of fibrinogen: This test is done with the objective of verifying if there is a sufficient amount of fibrinogen that can be used to generate fibrin.
In addition to these tests, the doctor may recommend others, such as the measurement of clotting factors, for example, so that it is possible to know if there is a deficiency in any clotting factor that may interfere with the hemostasis process.
