In a living heart or blood vessel, certain components in the blood coagulate or coagulate to form a solid mass, which is called thrombosis. The solid mass that forms is called a thrombus.
Under normal circumstances, there are coagulation system and anticoagulation system (fibrinolysis system, or fibrinolysis system for short) in the blood, and a dynamic balance is maintained between the two, so as to ensure that the blood circulates in the cardiovascular system in a liquid state. constant flow
The coagulation factors in the blood are continuously activated, and a small amount of thrombin is produced to form a small amount of fibrin, which is deposited on the intima of the blood vessel, and then dissolved by the activated fibrinolytic system. At the same time, the activated coagulation factors are also continuously phagocytosed and cleared by the mononuclear macrophage system.
However, under pathological conditions, the dynamic balance between coagulation and anticoagulation is disrupted, the activity of the coagulation system is dominant, and blood coagulates in the cardiovascular system to form thrombus.
Thrombosis usually has the following three conditions:
1. Heart and blood vessel intima injury
The intima of normal heart and blood vessels is intact and smooth, and the intact endothelial cells can inhibit platelet adhesion and anticoagulation. When the inner membrane is damaged, the coagulation system can be activated in many ways.
The first damaged intima releases tissue coagulation factor (coagulation factor III), which activates the extrinsic coagulation system.
Secondly, after the intima is damaged, the endothelial cells undergo degeneration, necrosis, and shedding, exposing the collagen fibers under the endothelium, thereby activating the coagulation factor XII of the endogenous coagulation system and starting the endogenous coagulation system. In addition, the damaged intima becomes rough, which is conducive to platelet deposition and adhesion. After the adhered platelets rupture, a variety of platelet factors are released, and the entire coagulation process is activated, causing blood to coagulate and form a thrombus.
Various physical, chemical and biological factors can cause damage to the cardiovascular intima, such as endocarditis in swine erysipelas, pulmonary vasculitis in bovine pneumonia, equine parasitic arteritis, repeated injections in the same part of the vein, Injury and puncture of the blood vessel wall during surgery.
2. Changes in blood flow status
Mainly refers to slow blood flow, vortex formation and blood flow cessation.
Under normal circumstances, the blood flow rate is fast, and red blood cells, platelets and other components are concentrated in the center of the blood vessel, which is called axial flow; when the blood flow rate slows down, red blood cells and platelets will flow close to the blood vessel wall, called side flow, which increases thrombosis. risk that arises.
The blood flow is slowed down, and the endothelial cells are severely hypoxic, causing the degeneration and necrosis of the endothelial cells, the loss of their function of synthesizing and releasing anticoagulant factors, and the exposure of collagen, which activates the coagulation system and promotes thrombosis.
Slow blood flow can also make the formed thrombus easy to fix on the blood vessel wall and continue to increase.
Therefore, thrombus often occurs in veins with slow blood flow and prone to eddy currents (at the venous valves). Aortic blood flow is fast, and thrombus is rarely seen. According to statistics, the occurrence of venous thrombosis is 4 times more than that of arterial thrombosis, and venous thrombosis often occurs in heart failure, after surgery or in sick animals lying in the nest for a long time.
Therefore, it is of great significance to help sick animals who have been lying down for a long time and after surgery to do some appropriate activities to prevent thrombosis
3. Changes in blood properties.
Mainly refers to increased blood coagulation. Such as extensive burns, dehydration, etc. to concentrate blood, severe trauma, postpartum, and severe blood loss after major operations can increase the number of platelets in blood, increase blood viscosity, and increase the content of fibrinogen, thrombin and other coagulation factors in plasma Increase. These factors can promote thrombosis.
Summary
The above three factors often coexist in the process of thrombosis and affect each other, but a certain factor plays a major role in different stages of thrombosis.
Therefore, in clinical practice, it is possible to prevent thrombosis by correctly grasping the conditions of thrombosis and taking corresponding measures according to the actual situation. Such as the surgical process should pay attention to gentle operation, should try to avoid damage to blood vessels. For long-term intravenous injection, avoid using the same site, etc.
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