Thrombosis is the lifetime loss of dense masses (blood clots) from the blood, which are fixed on the inner wall of the vessel or heart and more or less interfere with the flow of blood. A blood clot consists of erythrocytes , leukocytes, blood platelets ( platelets ) and fibrin in different ratios. There are coagulative thrombi, which are based on the usual mechanisms of blood coagulation (see. Blood clotting ), and agglutination (precipitational) thrombi, which are formed from blood plates upon sedimentation and gluing them on the inner surface of the vessel, followed by disintegration. An initially coagulation agglutination thrombus may build up. Depending on the composition, blood clots are distinguished: red, white and mixed (layered). A red blood clot, usually coagulative, consists of a fibrinous network, which contains blood cells, white - from fibrin, platelets, leukocytes. Often, the initial part of a blood clot (its head) is represented only by platelets and is white in color, while the next part extending along the axis of the vessel is red.
Thrombotic masses are dry, often crumbling, associated with the inner surface of the vessel; in this they differ from easily retrieved succulent post-mortem blood clots .
Blood clots can form in all parts of the cardiovascular system : heart cavities, arteries, veins, capillaries. In the heart, they are formed most often in ventricular aneurysms after heart attacks, in the atria - with valvular defects. In the aorta and arteries - with ulcerative atherosclerosis, in the aortic aneurysm . In the veins - with varicose dilatation, prolonged stagnation.Go
Thrombosis is observed in many diseases as a complicating general pathological process, sometimes thrombosis forms the basis of the disease and causes a special nosological form - thromboembolic disease (see).
The causes of thrombosis are varied, however, three conditions are necessary: damage to the vascular wall, impaired blood flow, in particular its deceleration, changes in the blood (clotting, etc.), resulting in loss of dense masses. With rapid blood flow, blood clots are not formed even with a significant damage to the vessel wall; contribute to the formation of thrombosis of turbulence of blood flow (for example, in aneurysms) and other obstacles to blood flow.
There are near-wall thrombi, which occupy only part of the vessel lumen, and occlusive, filling the entire lumen.
The outcome of a blood clot is different; the most favorable is the aseptic melting of a blood clot by proteolytic enzymes , thereby allowing the vessel's patency to be restored; another outcome is the organization of a blood clot with its invasion of the connective tissue and tight fixation on the inner surface of the vessel. Subsequently, channels lined by the endothelium are formed in such a thrombus, and it turns into a spongy tissue through which blood flow can be restored (drainage of the thrombus). An unfavorable outcome is the separation of thrombotic masses with subsequent embolism (see) or purulent fusion of a blood clot in contact with pyogenic bacteria with the development of septicopyemia (see Sepsis ). Thrombi in the large veins (pelvic, lower extremities), as well as thrombus of the right atrium (for example, with mitral disease) are dangerous due to the threat of pulmonary embolism; blood clots from the left atrium are the source of embolism of the brain, kidney, intestine, lower extremities.
The clinical picture of thrombosis of large venous trunks, such as veins of the limbs, pelvis, and inferior vena cava, depends on the location of the thrombus, the degree of concomitant vasospasm, the presence of inflammation, etc. (see Thrombophlebitis ).
Fig. 1. Parietal thrombus of the aorta. Fig. 2. Mixed continuous aortic thrombus: 1 - thrombus head; 2 - the body of a blood clot; 3 - thrombus tail. Fig. 3. Parietal white thrombus: 1 — leukocytes and masses of adhered plates; 2 - fibrin filaments; 3 - vessel wall. Fig. 4. Organization with sewage clot: 1 - channels lined by endothelium; 2 - organized thrombotic masses; 3 - vessel wall. Fig. 5. Organization with vascularization of a thrombus (dyeing for elastic fibers): 1 - newly formed vessels; 2 - organized thrombotic masses; 3 - vessel wall.