CVP Unit I - 1 CV P Unit 1 Study Guide Ch ap ter 36 Hemo st...

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1 CV P Unit 1 Study Guide Ch ap ter 36: Hemo st asi s and Blo od Co agul atio n: Eve nts in He mos ta si s: § hemostasis – prevention of blood loss § achieved by: § vascular spasm § formation of a platelet plug § formation of a blood clot as a result of blood coagulation § eventual growth of fibrous tissue into the blood clot to close the hole in the vessel permanently § the trauma to a blood vessel begins the process of vascular contraction: § contraction is from nervous reflexes, local myogenic spasm, and local humoral factors from the traumatized tissues and blood platelets § nervous reflexes are initiated by pain nerve impulses (or other impulses from the vessel or nearby tissue) § most vasoconstriction results from local myogenic contraction of the blood vessels initiated by damage to the wall § in smaller vessels – platelets are responsible for most of the vasoconstriction by releasing thr omboxane A2 § more trauma to a vessel causes more spasm § a sharply cut vessel bleeds more than a crushed vessel § local spasm can last for minutes or hours – this allows for platelet plugging and blood coagulation § platelet plug can fill a small hole in a blood vessel: § platelets change their characteristics § begin to swell § assume irregular forms with numerous irradiating pseudopods § contractile proteins contract forcefully – causes release of granules that contain multiple active factors § become sticky – adhere to collagen in the tissues and to a protein called von Willebrand factor – spreads throughout the plasma § secrete large amounts of ADP § enzymes form thromboxane A2 § ADP and thromboxane act on nearby platelets to activate them § stickiness of the additional platelets causes them to adhere to the original platelets § formation of the blood clot is the third mechanism for hemostasis: § 3 rd mechanism for hemostasis is formation of a blood clot § clot begins to develop in 15-20 seconds if the trauma has been severe § develops in 1-2 minutes if the trauma is minor § activator substances from the traumatized vascular wall, platelets, and from blood proteins adhering to the traumatized vascular wall initiate the clotting process § within 3-6 minutes after the rupture of a vessel (if the opening is not too large) the entire opening or broken end is filled with clot § after 20-60 minutes, the clot retracts, closing the vessel even further Me cha ni sm of Blood Coa gula tion : General Mechanism: § clotting occurs in 3 essential steps:
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2 § prothrombin activator – complex of substances formed in response to rupture or damage to the blood vessel § prothrombin activator catalyzes the conversion of prothrombin into thrombin § thrombin acts as an enzyme to convert fibrinogen into fibrin threads to enmesh platelets, blood cells, and plasma to form the clot Conversion of Prothrombin to Thrombin: § prothrombin is an unstable plasma protein that can easily split into smaller compounds – one is thrombin §
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