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Blood coagulation is the process that causes blood to clot and helps prevent excessive blood loss when a vein or artery is pierced or broken.
Blood coagulation is the body's natural way of preventing its blood supply from being lost through a cut, puncture, or other trauma to blood vessels. All of the components necessary for coagulation are found in the blood. The coagulation process involves a series of proteins, protein cofactors, and enzymes that interact on membrane surfaces. It is normally activated by damaged tissue.
Normal blood coagulation is a complex process that involves 20 to 30 components, called blood coagulation factors, and a series of complex chemical reactions. When a blood vessel is injured, platelets in the area of the damage clump together and stick to the edges of the cut to begin the coagulation process. Platelets are fragments of cells containing clotting factors. These clotting factors combine with a protein called prothrombin in a reaction that converts prothrombin to thrombin. Thrombin then converts fibrinogen (a protein present in plasma) into long, sticky threads of another protein called fibrin. The fibrin forms a mesh-like net over the opening and traps red blood cells as they try to leak out of the cut. As the clot hardens, it forms a protective seal over the cut.
The platelets also release messengers into the blood that perform additional functions including: constriction of the damaged blood vessels to reduce bleeding, attracting more platelets to the injury site to enlarge the clot, and activating other clotting factors, such as fibrinogen.
The ability of the blood to form a self-sealing clot when a blood vessel is injured is crucial. Without coagulation, a cut or puncture wound, no matter how minor, would continue to bleed and quickly lead to death. A deficiency in any of the protein coagulation factors can result in hemorrhages following injury. In some coagulation disorders, such as hemophilia, the deficiency is due to an inherited defect. In others, the deficiency is due to an acquired condition, such as vitamin K deficiency.
Author Info: Ken R. Wells, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Nursing and Allied Health, 2002
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