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A clotting mechanism is the series of chemical processes that occur in the body and that lead to the formation of a clot. A clot is a collection of cells that seals and protects damaged areas of blood vessels while the body heals itself. Although a clot can form because there has been an injury, it also can form because of certain diseases or blood disorders. A clot is intended to stop bleeding and prevent infection as well as provide a safe area for healing to occur. After the area has been repaired, the clot dissolves back into the body.
When a blood vessel is damaged, the clotting mechanism begins when the walls of the vessel release certain unique proteins. These proteins send signals to a type of cell in the blood called a platelet. Platelets are created in the bone marrow and are the first cells to encounter the damaged area. They immediately converge on the injury and form a temporary barrier to seal the wound and stop the bleeding.
The next event to occur is the activation of the thrombin system. This is also called a clotting cascade. After this part of the blood clotting process begins, a series of chemical reactions occurs. Each reaction forms a new set of chemicals and proteins, which then react again. This cascade results in the formation of long strands of a substance called fibrin.
The fibrin moves to the area that the platelets have sealed. Strands of fibrin attach themselves over the platelets to strengthen and stabilize the clot. The combination of platelets and fibrin strands completes the formation of the clot, and the injury can begin to heal.
The clotting mechanism varies slightly depending on the type of blood vessel in which the process is occurring. In veins, the clots will be formed from more fibrin than platelets. In arteries, the clots are more platelets than fibrin.
Certain diseases can cause the clotting mechanism to malfunction. In these cases, a clot might form for no reason. The clot also might continue to amass platelets and fibrin until it is large enough to block the blood vessel.
Similarly, there are disorders such as hemophilia that interrupt the clotting mechanism and hinder the formation of clots. In a hemophiliac, the clotting pathway that forms fibrin is disrupted, and the clotting cascade is unable to begin. Without the fibrin to stabilize the temporary clot, the platelets are easily broken apart, and bleeding resumes.