MEDICAL BIOLOGY, ANATOMY, HUMAN PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

CHAPTER 1. ORGAN. ORGAN SYSTEM. ORGANISM

CIRCULATORY DISORDERS

6. THROMBOSIS

Thrombosis (from the Greek thrombos — Blood clot) is The process of intravascular Blood Coagulation during life within a blood vessel lumen or The Heart chambers, which obstructs normal blood flow.

The conditions predisposing to thrombosis can be systemic or local. Among the systemic factors, the primary role belongs to the interaction between the procoagulant and anticoagulant systems, which maintains blood in a fluid state within The Vascular System. Furthermore, Changes in the qualitative COMPOSITION OF THE blood — specifically, elevated levels of fibrinogen and Lipids, as well as alterations in blood rheological properties associated with atherosclerosis or autoimmune diseases — are of major significance.

Local factors of thrombosis include changes in the vascular walls and sluggish blood flow. Structural alterations of the vessel wall are accompanied by changes in The surface of the intima (the inner lining of the vessel wall), which promotes platelet adhesion, as well as disruption of laminar BLOOD FLOW IN areas of injury.

Thrombosis is an intravital process and differs from postmortem blood clotting by several distinct features: thrombi are always firmly attached to the vessel walls, have a dense consistency, and possess a characteristic surface Morphology and color. The bulk of a thrombus consists of fibrin, within the meshwork of which platelets, erythrocytes, and leukocytes are entrapped. Depending on the predominance of specific structural components and gross appearance, white, red, and mixed thrombi are distinguished.

A white thrombus is composed of fibrin, platelets, and leukocytes; it forms slowly under conditions of rapid blood flow (most commonly in Arteries).

A red thrombus consists of a fibrin meshwork enclosing erythrocytes with a small number of leukocytes. It develops more frequently within the lumen of Veins.

A mixed thrombus is a combination of white and red thrombi. It comprises a HEAD (white thrombus), a body (the mixed thrombus proper), and a tail (red thrombus).

Thrombi can be mural, which partially narrow the vascular lumen, or occlusive, which completely block it.

Outcomes of thrombosis:

1. Thrombus softening refers to the enzymatic liquefaction of dense protein masses by Enzymes released from leukocytes. The thrombus disintegrates, turning into a fine-grained mass composed of protein and lipid granules.

2. Thrombus Organization involves its replacement by young Connective Tissue with the subsequent formation of microchannels lined by endothelial Cells, a process known as canalization of the thrombus.

3. Thrombus petrification (calcification) is characterized by the deposition of calcium salts within the thrombus.

4. Purulent softening occurs when thrombosis develops secondary to an inflammatory process and is infected from the outset. In other cases, it results from the invasion of microorganisms circulating in the blood during Sepsis. This outcome is particularly dangerous as it can lead to the systemic spread of infection (generalization).

5. Thromboembolism is characterized by the detachment of a thrombus fragment (embolus), which is then carried throughout the body via the bloodstream.

The Clinical significance of thrombosis for the Organism is determined by its rate of onset, localization, extent, and ultimate outcomes. These outcomes can be favorable (aseptic softening, organization, petrification) or unfavorable (purulent softening of the thrombus, thromboembolism).