Hemostasis Hemoblood Stasisstanding still Stoppage of bleeding resulting

Hemostasis (Hemo-blood Stasis-standing still) § Stoppage of bleeding resulting from a break in a blood vessel § Hemostasis involves three phases 1. Vascular spasms 2. Platelet plug formation 3. Coagulation (blood clotting) Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings

Step One: Vascular spasms § Vasoconstriction causes blood vessel to spasm § Spasms narrow the blood vessel, decreasing blood loss Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings

Step 2: Platelet plug formation § Collagen fibers are exposed (because of the break in a blood vessel Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings

Step 2: Platelet plug formation § Chemical signals cause the platelets to become activated (sticky) and cling to collagen fibers § Anchored platelets release chemicals to attract more platelets § Platelets pile up to form a platelet plug Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings

Step 3: Coagulation § Injured tissues release tissue factor (TF) § protein clotting factors and calcium ions trigger a clotting cascade Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings

§ prothrombin is activated § prothrombin to thrombin (an enzyme) § thrombin builds fibrinogen proteins into hairlike molecules of fibrin (insoluable) § fibrin forms a meshwork (the basis for a clot) Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings

Summary of steps Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings

Hemostasis § Blood usually clots within 3 to 6 minutes § The clot remains as endothelium regenerates § The clot is broken down after tissue repair Copyright © 2009 Pearson Education, Inc. , publishing as Benjamin Cummings