Verihyytymisessä

Verihyytymisessä, also known as blood clotting or coagulation, is a vital physiological process that prevents excessive bleeding when a blood vessel is injured. This complex cascade involves a series of protein interactions, primarily driven by enzymes and substrates circulating in the blood. The ultimate goal is to form a stable fibrin clot that seals the damaged vessel wall.

The process begins with primary hemostasis, where platelets, small cell fragments, adhere to the site of injury and aggregate to form a platelet plug. This initial plug is often temporary and needs to be reinforced by a more robust fibrin clot.

Secondary hemostasis involves the coagulation cascade, a series of enzymatic reactions that culminate in the conversion of soluble fibrinogen into insoluble fibrin. This cascade can be initiated through two main pathways: the intrinsic pathway, activated by factors within the blood itself, and the extrinsic pathway, triggered by tissue factor released from damaged cells. Both pathways converge on a common pathway that leads to the activation of thrombin, the enzyme responsible for converting fibrinogen to fibrin. Fibrin then forms a meshwork that traps blood cells and platelets, creating a stable clot.

Once the bleeding is controlled and the vessel wall has healed, a process called fibrinolysis begins. This involves the breakdown of the fibrin clot by enzymes like plasmin, ensuring that blood flow is restored and no unnecessary clots remain. Disruptions in this intricate system can lead to either excessive bleeding disorders, such as hemophilia, or to the formation of unwanted blood clots, known as thrombosis, which can cause serious conditions like heart attacks and strokes.