Hemostasis Essay

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Khang Bui Test 1 Essay Hemostasis has three mechanisms to help prevent blood loss, which is vascular spasm, platelet plug formation, and blood clotting (coagulation). Vascular Spasm is the most immediate protection against blood loss. Injury to the vessel causes smooth muscle to contract (vasoconstriction) to reduce the amount of blood flow through the area and reduce the amount of blood loss. Thus, the vascular spasm helps maintain hemostasis long enough for the other to come into play Platelet plug formation has three stages; Adhesion, Release Reaction and Aggregation. Adhesion of platelets is stimulated by the damage tissue; Platelets do not adhere to the endothelium that lines healthy blood vessels and the heart. The endothelium is very smooth and coated with prostacyclin. Release reaction is when the platelets grow long pseudopods that adhere to the vessels and to other platelets. They will contract, draw the wall of vessel together and the platelets will aggregate. Therefore, platelets undergo degranulation the exocytosis of their cytoplasmic granules and release of factors that promote hemostasis. Aggregation is occurs when serotonin (vasoconstrictor), ADP (attracts more platelets and stimulates their degranulation), and thromboxane A2 (stimulates degranulation and vasoconstriction) are released. Thus it can quickly seal a small break in blood vessel. Coagulation is the last process of the hemostasis. It has three ways; intrinsic, extrinsic and common pathways. The Intrinsic pathway is more complex and slower than the extrinsic pathway and the activator is direct contact with blood leading to prothrombinase formation. The Extrinsic pathway is occurs rapidly as Thromboplastin leaks into the blood from cell outside blood vessels and initiates formation of prothrombinase. The Common pathway starts when prothrombinase (with Ca2+ present) converts

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