Describe the steps involved in hemostasis. Compare the extrinsic and intrinsic pathways of coagulation
What will be an ideal response?
Hemostasis or the prevention of blood loss from a damaged vessel involves three major phases: vascular spasm, platelet aggregation to form a plug, and clot formation. The vascular spasm is vasoconstriction stimulated by chemicals released from the injured vessel. This reduces blood flow through the injured vessel, reducing blood loss. Platelets adhere to the injured vessel and then release chemicals to attract other platelets to the injury. This aggregation of platelets forms a temporary plug at the site of the injury. In addition to forming a plug, the platelets release chemicals to enhance the coagulation process that leads to clot formation. The coagulation process is activated by two pathways, the intrinsic and extrinsic pathways. The intrinsic pathway is a slower process that is initiated when clotting factor XII is activated when exposed to collagen from an injured vessel. The shorter extrinsic pathway is activated when tissue factors external to the blood are released into the blood when the tissue is traumatized. Tissue thromboplastin activates clotting factor X, skipping many of the steps associated with the intrinsic pathway. Both pathways ultimately activate thrombin, which converts fibrinogen into fibrin, which then forms a stable meshwork or clot.
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