Business Due in Lab PreLab #8 Priority registration is Thursday 2/28/13 Midterm 2 is Monday 3/4/13 Study Guide posted Cardiovascular System BLOOD CLOTTING Platelets Stem cell Developmental pathway Hemocyto- Promegakaryocyte blast Megakaryoblast Megakaryocyte Platelets Figure 17.12 Hemostasis Fast series of reactions for stoppage of bleeding 1. Vascular spasm 2. Platelet plug formation 3. Coagulation (blood clotting) Vascular Spasm Vasoconstriction of damaged blood vessel Triggered by Direct injury Chemicals released by endothelial cells and platelets Platelet Plug Platelets attracted to injured vessel wall Collagen and glycoprotein Actin and myosin Step 1 Vascular spasm • Smooth muscle contracts, causing vasoconstriction. Step 2 Platelet plug formation • Injury to lining of vessel Collagen exposes collagen fibers; fibers platelets adhere. • Platelets release chemicals that make nearby platelets sticky; platelet plug forms. Platelets Step 3 Coagulation • Fibrin forms a mesh that traps red blood cells and platelets, forming the clot. Fibrin Figure 17.13 Coagulation Blood is transformed from a liquid to a gel Reinforces platelet plug Coagulation Damaged cells release Thromboplastin Prothrombin Thrombin Fibrinogen Fibrin Figure 17.15 Clinical Considerations Bleeding disorders Prevent normal clot formation Thromboembolic disorders Undesirable clot formation Bleeding Disorders Hemophilia Several similar hereditary bleeding disorders Symptoms Prolonged bleeding Treated Plasma transfusions Injection of missing factors Bleeding Disorders Thrombocytopenia Deficiency of circulating platelets Causes Bone marrow disease Symptoms Spontaneous bleeding petechiae Treatment Transfusion of concentrated platelets Thromboembolytic Conditions Thrombus: clot that develops and persists in an unbroken blood vessel May block circulation, leading to tissue death Embolus: a thrombus freely floating in the blood stream Pulmonary emboli Cerebral emboli Thromboembolytic Conditions Atherosclerosis, inflammation, sedentary states Prevention Aspirin Heparin Warfarin (Coumadin) .