Hemostasis and Bleeding Disorders PDF

‫سورة البقرة آية ‪32‬‬  Delineate the process of hemostasis that restricts blood loss when vessels are damaged. Describe the natural anticlotting mechanisms. Describe different forms of bleeding disorders.  Hemostasis Definition: It is the process of formin...

‫سورة البقرة آية ‪32‬‬  Delineate the process of hemostasis that restricts blood loss when vessels are damaged. Describe the natural anticlotting mechanisms. Describe different forms of bleeding disorders.  Hemostasis Definition: It is the process of forming clots in the walls of damaged blood vessels (small cut) & preventing blood loss while maintaining blood in a fluid state within the vascular system. Mechanism: ▪. Constriction of blood vessel ▪. Platelet reaction or formation of platelet plug ▪. Blood coagulation to form the blood clot.  Hemostasis A-Constriction of blood vessel: It occurs immediately after injury Causes of VC: A.Nervous reflex initiated by pain from the traumatized vessel B.Myogenic contraction due to direct trauma C.Local humoral factors released by platelets as serotonin & thromboxan A2.  Hemostasis B-Platelet reaction: 1-Platelet adhesion:. When the vascular surface are damaged → platelet adhere to the sub- endothelial collagen of injured vessels. This adhesion depends on Von- Willebrand factor. 2-Platelet activation:. Binding of platelets to collagen initiates the platelet activation which discharge their contents including ADP. ADP + Thrombin formed at the site of injury → activate the nearby platelets.  Hemostasis B-Platelet reaction: 3-Release reaction of platelet: After platelet adhesion, they discharge their contents including: Serotonin ADP Thromboxan A2 4-Platelet aggregation: Which is mediated by: ADP Thromboxan A2 Platelet activation factor (PAF).  Hemostasis B-Platelet reaction: 5-Platelet fusion: It is irreversible fusion of aggregated platelets at the site of injury It is caused by:. High concentration of ADP. Platelets release retractozyme leading to clot retraction. Growth factor.  Hemostasis B-Platelet reaction: 6-Conversion of plug into the definitive clot: The platelet plug becomes firm when the fibrin threads are deposited to form the blood clot. After few minutes this clot starts to shrink. Hemostasis  Hemostasis C-Blood coagulation: It is the conversion of the soluble protein fibrinogen into insoluble fibrin threads entrapping blood cells & plasma ‫ ٭‬This conversion is catalyzed by thrombin ‫ ٭‬Thrombin is formed from its precursor prothrombin by the action of activated factor X ‫ ٭‬Activation of factor X occurs by: Intrinsic system Extrinsic system.  Anticlotting System Factors that oppose clot: 1-Prostacyclin ( platelet aggregation and phospholipids release that initiate coagulation). 2-Protein C. (deactivates factor V, VIII) 3-Antithrombin III (inactivates thrombin via binding with heparin)  The Fibrinolytic System Definition: The principal mechanism of clot removal (dissolve clot). It is activated simultaneously with the coagulation mechanism, it restricts clotting to a limited area → prevent excess intravascular coagulation.  Plasminogen Activators 1-XIIa 2-Components from injured tissues 3-Thrombin Plasminogen Plasmin Fibrin Soluble fibrin fragments* Purpura  Vitamin K Synthesis of: Factor II Factor VII Factor IX Factor X